Urethane-modified prepolymers containing pendent alkyl groups, compositions and uses thereof

ABSTRACT

Adducts and prepolymers comprising pendent alkyl groups are disclosed. Polythiol adducts prepared by reacting a polythiol with a ketone and urethane-extended polythiol adducts. The polythiol adducts can be terminated with isocyanate groups. Compositions comprising the isocyanate-terminated polythiol adducts, isocyanate-terminated sulfur-containing prepolymers, and diisocyanates can be combined with polyamine or polyepoxide curing agents to provide curable compositions. Cured compositions are suitable for aerospace coating and sealant applications. The compositions can also include a low specific gravity filler and, when cured, meet the requirements of aerospace sealant applications.

This application is a divisional of U.S. application Ser. No. 14/937,904filed on Nov. 11, 2015, now allowed, which is incorporated by referencein its entirety.

FIELD

The invention relates to polythiol adducts prepared by reacting apolythiol with a ketone and urethane-extended polythiol adducts. Thepolythiol adducts can be terminated with isocyanate groups. Compositionscomprising the isocyanate-terminated polythiol adducts,isocyanate-terminated sulfur-containing prepolymers, and diisocyanatescan be combined with polyamine or polyepoxide curing agents to providecurable compositions. Cured compositions are suitable for aerospacecoating and sealant applications. The compositions can also include alow specific gravity filler and, when cured, meet the requirements ofaerospace sealant applications.

BACKGROUND

Coatings and sealants used in the aerospace industry must meet demandingperformance requirements. The coatings and sealants must exhibitexcellent initial adhesion, tensile strength and elongation and mustmaintain acceptably high values following exposure to aviation fluids,high temperature, and/or salt spray. In addition, to reduce the weightof aerospace vehicles it is also desirable that aerospace coatings andsealants exhibit a low specific gravity.

Aerospace compositions having a low specific gravity can include a highloading of low density filler. The addition of a high volume or weightpercent of a low density filler can increase the viscosity of theuncured composition to an extent that the ability to apply thecomposition and/or the useful working time of the composition is notacceptable. To provide homogeneous properties, it is also important thata filler be uniformly dispersed throughout the coating or sealant.

Low density aerospace coatings and sealants having homogenouslydispersed fillers, improved adhesion, and enhanced flexibility aredesired.

SUMMARY

Isocyanate-terminated urethane-containing prepolymers of the presentinvention can be combined with a polyamine curing agent and a lowdensity filler to provide low density coatings and sealants that meetthe requirements of aerospace sealant applications. Theisocyanate-terminated urethane-containing prepolymers can be prepared byreacting a diisocyanate, a polythiol adduct, and a thiol-terminatedsulfur-containing prepolymer.

According to the present invention, polythiol adducts can comprise thecondensation reaction products of reactants comprising a polythiol and aketone.

According to the present invention, polythiol adducts can have thestructure of Formula (6):

HS—(—R¹—S—R²—S—)_(n)—R¹—SH  (6)

wherein,

-   -   n is an integer from 1 to 10;    -   each R¹ independently comprises a moiety of Formula (1a):

—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a)

-   -   -   wherein,            -   each R³ comprises hydrogen or methyl;            -   each X is independently selected from O and S;            -   p is an integer from 2 to 6;            -   q is an integer from 1 to 5; and            -   r is an integer from 2 to 10; and

    -   each R² independently is a moiety having the structure of        Formula (3a):

—C(—R⁴)₂—  (3a)

-   -   -   wherein each R⁴ independently comprises C₁₋₅ alkyl.

According to the present invention, urethane-extended polythiol adductscan comprise the reaction product of reactants comprising: a polythioladduct provided by the present disclosure; and a diisocyanate.

According to the present invention, urethane-extended polythiol adductscan have the structure of Formula (7):

HS-[-A-S—C(═O)—NH—R⁵—NH—C(═O)—S—]_(m)-A-SH  (7)

wherein,

-   -   each R⁵ independently comprises a core of a diisocyanate;    -   m is an integer from 1 to 10;    -   each A independently comprises a moiety having the structure of        Formula (6a):

—(—R¹—S—R²—S—)_(n)—R¹—  (6a)

-   -   wherein,        -   n is an integer from 1 to 10;        -   each R¹ independently comprises a structure of Formula (1a):

—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a)

-   -   -   -   wherein,                -   each R³ comprises hydrogen or methyl;                -   each X is independently selected from O and S;                -   p is an integer from 2 to 6;                -   q is an integer from 1 to 5; and                -   r is an integer from 2 to 10; and

        -   each R² independently comprises a moiety having the            structure of Formula (3a):

—C(—R⁴)₂—  (3a)

-   -   -   -   wherein each R⁴ independently comprises C₁₋₅ alkyl.

According to the present invention, isocyanate-terminatedurethane-containing prepolymers can comprise the reaction product ofreactants comprising: the polythiol adduct provided by the presentdisclosure; a thiol-terminated sulfur-containing prepolymer; and adiisocyanate.

According to the present invention, isocyanate-terminatedurethane-containing prepolymers can comprise the reaction products ofreactants comprising: an isocyanate-terminated sulfur-containingprepolymer, a polythiol adduct, and a diisocyanate; wherein, theisocyanate-terminated prepolymer comprises the reaction product ofreactants comprising a diisocyanate and a thiol-terminatedsulfur-containing prepolymer; and the polythiol adduct comprises thepolythiol adduct provided by the present disclosure.

According to the present invention, isocyanate-terminatedurethane-containing prepolymers can comprise an isocyanate-terminatedurethane-containing prepolymer of Formula (15a), anisocyanate-terminated urethane-containing prepolymer of Formula (15b),or a combination thereof:

D-S—P—S-D  (15a)

{D-S—P—S—V′—}_(z)B  (15b)

wherein,

-   -   each D independently comprises a moiety having the structure of        Formula (16a), Formula (16b), Formula (16c), Formula (16d),        Formula (16e), Formula (16f), Formula (16g), or a combination of        any of the foregoing:

—C(═O)—NH—R⁵—N═C═O  (16a)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O  (16b)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—N═C═O}_(z-1)  (16c)

—C(═O)—NH—R⁵—{—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—}_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16d)

—C(═O)—NH—R⁵—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—N═C═O}_(z-1)  (16e)

—C(═O)—NH—R⁵—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16f)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16g)

wherein,

-   -   each R⁵ independently comprises a core of a diisocyanate;    -   each m is an integer from 1 to 10;    -   each E comprises a core of a polythiol adduct;    -   each P comprises a polythioether moiety or a polysulfide moiety;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol; and    -   each —V′— is derived from the reaction of —V with a thiol.

According to the present invention, isocyanate-terminatedurethane-containing prepolymers can comprise an isocyanate-terminatedurethane-containing prepolymer of Formula (19):

{D-S—}₃G  (19)

wherein,

-   -   G is a moiety of Formula (9d):

{—(—R⁶—S—S—)_(a)—CH₂—}₂CH—(—S—S—R⁶—)_(a)—  (9d)

-   -   wherein,        -   each a is independently an integer from 1 to 50;        -   the sum of each a is an integer from 5 to 60; and        -   each R⁶ comprises a moiety having the structure            —(CH₂)₂—O—CH₂—O—(CH₂)₂—; and    -   each D independently comprises a moiety having the structure of        Formula (20a), Formula (20b), Formula (20c) or Formula (20d):

—C(═O)—NH—R⁵—N═C═O  (20a)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O  (20b)

—C(═O)—NH—R⁵—NH—C(═O)—S-G{—S-D′}₂   (20c)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S-G{—S-D′}₂  (20d)

-   -   wherein,        -   each R⁵ independently comprises a core of a diisocyanate;            and        -   each m is an integer from 1 to 10;        -   each E comprises a core of a polythiol adduct or a core of a            urethane-containing polythiol adduct; and        -   each D′ comprises a moiety of Formula (20a) or a moiety of            Formula (20b).

According to the present invention, compositions can comprise anisocyanate-terminated urethane-containing prepolymer provided by thepresent disclosure.

According to the present invention, parts can comprise a sealantprepared from a composition of composition provided by the presentdisclosure.

According to the present invention, methods of sealing a part cancomprise: providing a curable composition comprising the compositionprovided by the present disclosure; applying the curable composition toat least a portion of a surface of a part; and curing the appliedcurable composition to seal the part.

Reference is now made to certain compounds, compositions, sealants, andmethods of the present invention. The disclosed compounds, compositions,sealants, and methods are not intended to be limiting of the claims. Tothe contrary, the claims are intended to cover all alternatives,modifications, and equivalents.

DETAILED DESCRIPTION

For purposes of the following description, it is to be understood thatembodiments provided by the present disclosure may assume variousalternative variations and step sequences, except where expresslyspecified to the contrary. Moreover, other than in the examples, orwhere otherwise indicated, all numbers expressing, for example,quantities of ingredients used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that may vary depending upon the desired properties to beobtained. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges encompassed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of about 1 and the recited maximumvalue of about 10, that is, having a minimum value equal to or greaterthan about 1 and a maximum value of equal to or less than about 10.

Also, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

A dash (“-”) that is not between two letters or symbols is used toindicate a point of bonding for a substituent or between two atoms. Forexample, —CONH₂ is bonded to another chemical moiety through the carbonatom.

“Alkyl” refers to a mono-radical of a saturated, branched orstraight-chain, acyclic hydrocarbon group having, for example, from 1 to20 carbon atoms, from 1 to 10 carbon atoms, from 1 to 6 carbon atoms,from 1 to 4 carbon atoms, or from 1 to 3 carbon atoms. It will beappreciated that a branched alkyl has a minimum of three carbon atoms.An alkyl group can be C₂₋₆ alkyl, C₂₋₄ alkyl, or, C₂₋₃ alkyl. Examplesof alkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, tert-butyl, n-hexyl, n-decyl, tetradecyl, and the like. Analkyl group is C₂₋₆ alkyl, C₂₋₄ alkyl, or C₂₋₃ alkyl. It will beappreciated that a branched alkyl has at least three carbon atoms.

“Alkanediyl” refers to a diradical of a saturated, branched orstraight-chain, acyclic hydrocarbon group, having, for example, from 1to 18 carbon atoms (C₁₋₁₈), from 1-14 carbon atoms (C₁₋₁₄), from 1-6carbon atoms (C₁₋₆), from 1 to 4 carbon atoms (C₁₋₄), or from 1 to 3hydrocarbon atoms (C₁₋₃). It will be appreciated that a branchedalkanediyl has a minimum of three carbon atoms. The alkanediyl can beC₂₋₁₄ alkanediyl, C₂₋₁₀ alkanediyl, C₂₋₈ alkanediyl, C₂₋₆ alkanediyl,C₂₋₄ alkanediyl, or C₂₋₃ alkanediyl. Examples of alkanediyl groupsinclude methane-diyl (—CH₂—), ethane-1,2-diyl (—CH₂CH₂—),propane-1,3-diyl and iso-propane-1,2-diyl (e.g., —CH₂CH₂CH₂— and—CH(CH₃)CH₂—), butane-1,4-diyl (—CH₂CH₂CH₂CH₂—), pentane-1,5-diyl(—CH₂CH₂CH₂CH₂CH₂—), hexane-1,6-diyl (—CH₂CH₂CH₂CH₂CH₂CH₂—),heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl,dodecane-1,12-diyl, and the like. It will be appreciated that a branchedalkanediyl has at least three carbon atoms.

“Cycloalkanediyl” refers to a diradical saturated monocyclic orpolycyclic hydrocarbon group. The cycloalkanediyl group can be C₃₋₁₂cycloalkanediyl, C₃₋₈ cycloalkanediyl, C₃₋₆ cycloalkanediyl, or C₅₋₆cycloalkanediyl. Examples of cycloalkanediyl groups includecyclohexane-1,4-diyl, cyclohexane-1,3-diyl, and cyclohexane-1,2-diyl.

“Alkanecycloalkane” refers to a saturated hydrocarbon group having oneor more cycloalkyl and/or cycloalkanediyl groups and one or more alkyland/or alkanediyl groups, where cycloalkyl, cycloalkanediyl, alkyl, andalkanediyl are defined herein. The cycloalkyl and/or cycloalkanediylgroup(s) is C₃₋₆, C₅₋₆, and, cyclohexyl or cyclohexanediyl. The alkyland/or alkanediyl group(s) is C₁₋₆, C₁₋₄, C₁₋₃, or methyl, methanediyl,ethyl, or ethane-1,2-diyl. The alkanecycloalkane group is C₄₋₁₈alkanecycloalkane, C₄₋₁₆ alkanecycloalkane, C₄₋₁₂ alkanecycloalkane,C₄₋₈ alkanecycloalkane, C₆₋₁₂ alkanecycloalkane, C₆₋₁₀alkanecycloalkane, or C₆₋₉ alkanecycloalkane. Examples ofalkanecycloalkane groups include 1,1,3,3-tetramethylcyclohexane andcyclohexylmethane.

“Alkanecycloalkanediyl” refers to a diradical of an alkanecycloalkanegroup. The alkanecycloalkanediyl group is C₄₋₁₈ alkanecycloalkanediyl,C₄₋₁₆ alkanecycloalkanediyl, C₄₋₁₂ alkanecycloalkanediyl, C₄₋₈alkanecycloalkanediyl, C₆₋₁₂ alkanecycloalkanediyl, C₆₋₁₀alkanecycloalkanediyl, or C₆₋₉ alkanecycloalkanediyl. Examples ofalkanecycloalkanediyl groups include1,1,3,3-tetramethylcyclohexane-1,5-diyl and cyclohexylmethane-4,4′-diyl.

“Heterocycloalkanediyl” refers to a cycloalkanediyl group in which oneor more of the carbon atoms are replaced with a heteroatom, such as N,O, S, or P. In certain embodiments of heterocycloalkanediyl, theheteroatom is selected from N and O.

“Core of a diisocyanate” refers to the moiety between the twodiisocyanate groups of a diisocyanate. For example, for a diisocyanatehaving the general structure O═C═N—R—N═C═O, the moiety —R— representsthe core of the diisocyanate between the two isocyanate groups —N═C═O.As a further example, the core of the diisocyanate 4,4′-methylenedicyclohexyl diisocyanate (H₁₂MDI) having the structure:

is represented by the structure

A “curable composition” refers to a composition that comprises at leasttwo reactants capable of reacting to form a cured composition. Forexample, a curable composition can comprise a thiol-terminatedpolythioether prepolymer and a polyepoxide capable of reacting to form acured polymer network. A curable composition may include a catalyst forthe curing reaction and other components such as, for example, fillers,pigments, and adhesion promoters. The selection of the other componentscan be made as appropriate for a particular use such as formulated forsealant applications or formulated for coating applications. A curablecomposition may be curable at ambient conditions such as roomtemperature and humidity, or may require exposure to elevatedtemperature, moisture, or other condition(s) to initiate and/oraccelerate the curing reaction. A curable composition may initially beprovided as a two part composition including a base component and anaccelerator component. The base composition can contain one of thereactants participating in the curing reaction such as athiol-terminated polythioether prepolymer and the acceleratorcomposition can contain the other reactant such as a polyepoxide. Thetwo compositions can be mixed shortly before use to provide a curablecomposition. A curable composition can exhibit a viscosity suitable fora particular method of application. For example, a Class A sealantcomposition, which is suitable for brush-on applications can becharacterized by a viscosity from 150 Poise to 500 Poise. A Class Bsealant composition, which is suitable for fillet seal applications canbe characterized by a viscosity from 8,000 Poise to 16,000 Poise. AClass C sealant composition, which is suitable for fay seal applicationscan be characterized by a viscosity from 1,000 Poise to 4,000 Poise.After the two compositions are combined and mixed, the curing reactioncan proceed and the viscosity of the curable composition can increaseand at some point will no longer be workable. The period of time betweenwhen the two compositions are mixed to form the curable composition andwhen the curable composition can no longer be reasonably applied to asurface for its intended purpose is referred to as the working time. Ascan be appreciated, the working time can depend on a number of factorsincluding, for example, the curing chemistry, the application method,and the temperature. The working time can also be referred to as the potlife. Once a curable composition is applied to a surface (and duringapplication), the curing reaction proceeds to provide a curedcomposition. A cured composition develops a tack-free surfaces and fullycures over a period of time. This time period can be referred to as thecuring time. A curable composition can be considered to be cured whenthe surface is tack-free, or can be considered to be cured when theShore A hardness of the surface is 35A.

As used herein, “polymer” refers to oligomers, homopolymers, andcopolymers. Unless stated otherwise, molecular weights are numberaverage molecular weights for polymeric materials indicated as “Mn” asdetermined, for example, by gel permeation chromatography using apolystyrene standard in an art-recognized manner A polymer includes aprepolymer. A prepolymer such as a thiol-terminated polythioetherprepolymer provided by the present disclosure can be combined with acuring agent to provide a curable composition, which can cure to providea cured polymer network.

“Derived from the reaction of —V with a thiol” refers to a moiety —V′—that results from the reaction of a thiol group with a moiety comprisinga terminal group reactive with a thiol group. For example, a group V—can comprise CH₂═CH—CH₂—O—, where the terminal alkenyl group CH₂═CH— isreactive with a thiol group —SH. Upon reaction with a thiol group, themoiety —V′— is —CH₂—CH₂—CH₂—O—.

A “backbone of a polythioether prepolymer” refers to a polythioetherprepolymer between the terminal reactive groups. For example, a backboneof a polythioether prepolymer having the structure:

HS—R¹—[—S—(CH₂)₂—O—[—R²—O—]_(m)—(CH₂)₂—S—R¹—S—]_(n)—H

can have the structure:

—R¹—[—S—(CH₂)₂—O—[—R²—O—]_(m)—(CH₂)₂—S—R¹—S—]_(n)—.

A “polythioether moiety or a polysulfide moiety” refers to a moietycomprising multiple thioether —S— groups or disulfide groups —S—S—,respectively. A polythioether moiety can comprise the backbone of apolythioether prepolymer. A polysulfide moiety can comprise the backboneof a polythioether prepolymer.

A “core of a polythiol adduct or a core of a urethane-containingpolythiol adduct” refers to the segment of the polythiol adduct betweenthe reactive terminal groups. For example, the core of aurethane-containing polythiol adduct of Formula (6);

HS—(—R¹—S—R²—S—)_(s)—R¹—SH  (6)

has the structure of Formula (6a):

—(—R¹—S—R²—S—)_(s)—R¹—  (6a)

where s, R¹ and R² are defined herein. A core of a compound can also bereferred to as a backbone such as a backbone of an adduct or a backboneof a prepolymer.

A “polythiol adduct” comprises un-extended polythiol adducts andurethane-extended polythiol adducts. A un-extended polythiol adduct doesnot contain urethane segments within the adduct backbone and aurethane-extended polythiol adduct contains urethane segments within theadduct backbone. A polythiol adduct provided by the present disclosurecan comprise pendent alkyl groups in the adduct backbone.

A “urethane-containing polythiol adduct,” also referred to as aurethane-extended polythiol adduct can comprise one or more urethanesegments within the backbone of the polythiol adduct.

Compositions

Compositions according to the invention can comprise anisocyanate-terminated urethane-containing prepolymer. Theisocyanate-terminated urethane-containing prepolymer can comprisependent alkyl groups in the polymer backbone. The pendent alkyl groupscan interfere with a hydrogen bonding between polymer chains of thecomposition, thereby improving the flexibility of the cured composition.For example, the pendent alkyl groups can reduce the amount of hydrogenbonding between urethane and ester linkages between separate polymerchains, or even within a polymer chain. Pendent alkyl groups can alsolower the free energy of the composition thereby improving the spread ofthe composition onto a substrate surface and the adhesion of the coatingor sealant to the substrate. Pendent alkyl groups can also increase theflexibility of a cured coating or sealant by reducing the hard segmentdomain content of the cured polymer. Pendent alkyl groups can beincorporated into an isocyanate-terminated urethane-containingprepolymer using precursors such as polythiol adducts comprising pendentalkyl groups.

Isocyanate Prepolymer

An isocyanate-terminated urethane-containing prepolymer can comprise thereaction product of reactants comprising a polythiol adduct, athiol-terminated sulfur-containing prepolymer, and a diisocyanate.

Isocyanate-terminated urethane-containing prepolymers provided by thepresent disclosure can also be prepared by first reacting athiol-terminated sulfur-containing prepolymer or a combination ofthiol-terminated sulfur-containing prepolymers with a diisocyanate or acombination of diisocyanates to provide an isocyanate-terminatedsulfur-containing prepolymer; followed by reaction of theisocyanate-terminated sulfur-containing prepolymer with a polythioladduct and a diisocyanate.

Polythiol Adducts Un-Extended Polythiol Adducts

Polythiol adducts provided by the present disclosure can compriseun-extended polythiol adducts, urethane-extended polythiol adducts, orcombinations thereof. An un-extended polythiol adduct does not containurethane groups in the backbone. A urethane-extended polythiol adductcomprises urethane groups in the backbone of the adduct.

A polythiol adduct can comprise a dithiol adduct, a trithiol adduct, aurethane-extended dithiol adduct, a urethane-extended trithiol adduct,or a combination of any of the foregoing. Polythiol adducts can have athiol functionality, for example, from 2 to 6, from 2 to 5, or from 2 to4.

A polythiol adduct can comprise the reaction product of reactantscomprising a polythiol and a ketone. A polythiol adduct can comprisependent alkyl groups extending from the backbone of the adduct.

Examples of suitable polythiols for preparing a polythiol adduct includedithiols having the structure of Formula (1):

HS—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—SH  (1)

wherein,

-   -   each R³ comprises hydrogen or methyl;    -   each X is independently selected from O and S;    -   p is an integer from 2 to 6;    -   q is an integer from 1 to 5; and    -   r is an integer from 2 to 10.

In dithiols of Formula (1), each R³ can be hydrogen, X can be S, anddithiols have the structure of Formula (2a), or each R³ can be hydrogen,X can be O, and dithiols have the structure of Formula (2b):

HS—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—SH  (2a)

HS—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—SH  (2b)

In dithiols of Formula (1), Formula (2a), and Formula (2b), each R³ canbe hydrogen.

In dithiols of Formula (1), Formula (2a), and Formula (2b), at least oneR³ can be methyl.

In dithiols of Formula (1), Formula (2a), and Formula (2b), p can be 2,3, 4, 5, or 6.

In dithiols of Formula (1), Formula (2a), and Formula (2b), q can be 1,2, 3, 4, or 5.

In dithiols of Formula (1), Formula (2a), and Formula (2b), r can be 2,3, 4, 5, 6, 7, 8, 9, or 10.

In dithiols of Formula (1), Formula (2a), and Formula (2b), each R³ canbe hydrogen, p can be 2, q can be 2, and r can be 2.

In dithiols of Formula (1), Formula (2a), and Formula (2b), p can be 2,q can be 2, and r can be 2.

A polythiol can comprise a dithiol of Formula (2a), a dithiol of Formula(2b), or a combination thereof. A dithiol can comprisedimercaptodiethylsulfide (DMDS), 3,6-dioxa-1,8-octanedithiol (DMDO), ora combination thereof.

Ketones

Examples of suitable ketones for preparing a polythiol adduct includelow molecular weight ketones such as, propan-2-one, methyl ethyl ketone(butan-2-one), pentan-2-one, hexan-2-one, pentan-3-one,3-methylbutan-2-one, 3-methylpentan-2-one, 4-methylhexan-3-one,2-methylpentan-3-one, and 2,4-dimethylpentan-3-one. A ketone cancomprise methyl ethyl ketone. Higher molecular weight ketones may alsobe used.

Suitable ketones can have the structure of Formula (3):

R⁴—C(═O)—R⁴  (3)

where each R⁴ independently comprises C₁₋₅ alkyl.

In ketones of Formula (3), each R⁴ can independently comprise methyl,ethyl, n-propyl, n-butyl, n-pentyl, isopropyl, sec-butyl, pentan-2-yl,2-methylbutyl, isopentyl, 3-metylbutan-2-yl, or isobutyl.

In ketones of Formula (3), each R⁴ can independently comprise methyl orethyl. In ketones of Formula (3), one R⁴ can be methyl and the other R⁴can be ethyl, both R⁴ can be methyl, or both R⁴ can be ethyl.

A polythiol adduct can comprise the reaction product of a polythiol anda ketone such as the reaction product of a polythiol of Formula (1),Formula (2a), Formula (2b), or a combination of any of the foregoing;and a ketone of Formula (3).

Polythiol adducts can comprise dithiol adducts having the structure ofFormula (4):

H—{—S—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—SH  (4)

where X, p, q, r, R³ and R⁴ are defined as in Formula (1) and Formula(3), and n can be an integer from 1 to 10. For example, in polythioladducts of Formula (4), n can be an integer from 1 to 4, an integer from1 to 3, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

In polythiol adducts of Formula (4), X can be S and a polythiol adductcan have the structure of Formula (4a), X can be O and a polythioladduct can have the structure of Formula (4b), or can be a combinationthereof:

H—{—S—[—(CHR³)_(p)—S—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—S—]_(q)—(CHR³)_(r)—SH  (4a)

H—{—S—[—(CHR³)_(p)—O—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—O—]_(q)—(CHR³)_(r)—SH  (4b)

where p, q, r, R³ and R⁴ are defined as in Formula (1) and Formula (3),and n can be an integer from 1 to 10.

In polythiol adducts of Formula (4), Formula (4a), and Formula (4b), pcan be 2, q can be 2, r can be 2, each R⁴ can independently comprisemethyl or ethyl, and each R³ can be hydrogen.

When each R³ in polythiol adducts of Formula (4), Formula (4a), orFormula (4b), is hydrogen, a polythiol adduct can have the structure ofFormula (5), Formula (5a), or Formula (5b), respectively:

H—{—S—[—(CH₂)_(p)—X—]_(q)—(CH₂)_(r)—X—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—X—]_(q)—(CH₂)_(r)—SH  (5)

H—{—S—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—SH  (5a)

H—{—S—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—SH  (5b)

where X, p, q, r, n, and R⁴ are defined as in Formula (1), Formula (3),and Formula (4).

In polythiol adducts of Formula (5), Formula (5a), and Formula (5b), pcan be 2, q can be 2, r can be 2, and each R⁴ can independently comprisemethyl or ethyl.

A polythiol adduct can have the structure of Formula (6):

HS—(—R¹—S—R²—S—)_(s)—R¹—SH  (6)

wherein,

-   -   s is an integer from 1 to 10;    -   each R¹ independently comprises a moiety of Formula (1a):

—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a)

-   -   -   wherein,            -   each R³ is selected from hydrogen and methyl;            -   each X is independently selected from O and S;            -   p is an integer from 2 to 6;            -   q is an integer from 1 to 5; and            -   r is an integer from 2 to 10;

    -   each R² independently comprises a moiety having the structure of        Formula (3a):

—C(—R⁴)₂—  (3a)

-   -   -   wherein each R⁴ independently comprises C₁₋₅ alkyl.

In polythiol adducts of Formula (6), s can be from 1 to 6, from 1 to 5,from 1 to 4, from 1 to 3, from 1 to 2, or from 2 to 6. In polythioladducts of Formula (6), s can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

In polythiol adducts of Formula (6), each R³ can be hydrogen, q can be1, 2, or 3, r can be 2 or 3, and p can be 2 or 3.

Polythiol adducts can comprise the reaction product of a condensationreaction between a polythiol and a ketone. Polythiol adducts cancomprise the reaction product of reactants comprising DMDS and/or DMDO,and methyl ethyl ketone. The reaction can be catalyzed by an appropriatecatalyst such as para-toluene sulfonic acid. The mole ratio of polythiolto ketone can be selected to provide a desired number of pendent alkylgroups along the polythiol adduct backbone and/or to provide polythioladducts having a desired molecular weight.

Polythiol adducts provided by the present disclosure can becharacterized by a molecular weight, for example, from 250 Daltons to1,000 Daltons, from 300 Daltons to 800 Daltons, or from 350 Daltons to600 Daltons and can be liquid or solid at room temperature.

Urethane-Extended Polythiol Adducts

Polythiol adducts provided by the present disclosure can compriseurethane-extended polythiol adducts. Urethane-extended polythiol adductscomprise urethane groups in the backbone of the adduct.

Urethane-extended polythiol adducts can comprise the reaction productsof a polythiol adduct and a diisocyanate. Examples of suitable polythioladducts for preparing urethane-extended polythiol adducts include thosehaving the structure of Formula (4), Formula (4a), Formula (4b), Formula(5), Formula (5a), Formula (5b), and Formula (6). Examples of suitablediisocyanates for preparing urethane-extended polythiol adducts includealiphatic diisocyanates and aromatic diisocyanates.

Urethane-extended polythiol adducts can have the structure of Formula(7):

HS-(-A-S—C(═O)—NH—R⁵—NH—C(═O)—S—)_(m)-A-SH  (7)

wherein,

-   -   m is an integer from 1 to 10;    -   each A independently comprises a moiety having the structure of        Formula (6a):

—(—R¹—S—R²—S—)_(n)—R¹—  (6a)

-   -   wherein,        -   n is an integer from 1 to 10;        -   each R¹ independently comprises a structure of Formula (1a):

—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a)

-   -   -   -   wherein,                -   each R³ comprises hydrogen or methyl;                -   each X is independently selected from O and S;                -   p is an integer from 2 to 6;                -   q is an integer from 1 to 5; and

        -   r is an integer from 2 to 10;

        -   each R² independently comprises a moiety having the            structure of Formula (3a):

—C(—R⁴)₂—  (3a)

-   -   -   -   wherein each R⁴ independently comprises C₁₋₅ alkyl; and

        -   each R⁵ independently comprises a core of a diisocyanate.

In urethane-extended polythiol adducts of Formula (7), m can be aninteger from 1 to 10, from 1 to 8, from 1 to 6, from 1 to 4, or from 1to 3. In urethane-extended polythiol adducts of Formula (7), m can be 1,2, 3, 4, 5, 6, 7, 8, 9, or 10.

In urethane-extended polythiol adducts of Formula (7), each A cancomprise, for example, a moiety having the structure of Formula (6b),Formula (6c), Formula (6d), or Formula (6e):

—S—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—S—  (6b)

—S—[—(CH₂)₂—O—]_(q)—(CH₂)₂—S—  (6c)

—S—[—(CH₂)₂—S—]_(q)—(CH₂)₂—S—  (6d)

—S—[—(CH₂)₂—O—]_(q)—(CH₂)₂—S—  (6e)

where p, q, and r are defined as in Formula (1).

In urethane-extended polythiol adducts of Formula (7), each R⁴ canindependently comprise methyl, ethyl, n-propyl, n-butyl, n-pentyl,isopropyl, sec-butyl, pentan-2-yl, 2-methylbutyl, isopentyl,3-metylbutan-2-yl, or isobutyl. In urethane-extended polythiol adductsof Formula (7), each R⁴ can independently comprise methyl or ethyl.

Diisocyanates

Diisocyanates can be used to prepare urethane-extended polythiol adductsand prepolymers of the present disclosure.

For example, urethane-extended polythiol adducts provided by the presentdisclosure can be prepared by reacting a polythiol adduct with adiisocyanate.

A diisocyanate can comprise an aliphatic diisocyanate, an aromaticdiisocyanate, or a combination thereof.

Suitable diisocyanates include aliphatic diisocyanates such asisophorone diisocyanate (IPDI), tetramethyl xylene diisocyanate (TMX),4,4′-methylene dicyclohexyl diisocyanate (H₁₂MDI), methylene diphenyldiisocyanate (MDI), toluene diisocyanate (TDI), hexamethylenediisocyanate (HDI), and a combination of any of the foregoing.

Examples of other suitable aliphatic diisocyanates include1,6-hexamethylene diisocyanate (HDI), 1,5-diisocyanato-2-methylpentane,methyl-2,6-diisocyanatohexanoate, bis(isocyanatomethyl)cyclohexane,1,3-bis(isocyanatomethyl)cyclohexane, 2,2,4-trimethylhexane1,6-diisocyanate, 2,4,4-trimethylhexane 1,6-diisocyanate,2,5(6)-bis(isocyanatomethyl)cyclo[2.2.1.]heptane,1,3,3-trimethyl-1-(isocyanatomethyl)-5-isocyanatocyclohexane,1,8-diisocyanato-2,4-dimethyloctane,octahydro-4,7-methano-1H-indenedimethyl diisocyanate, and1,1′-methylenebis(4-isocyanatocyclohexane), and 4,4′-methylenedicyclohexyl diisocyanate (H₁₂MDI).

Examples of suitable alicyclic aliphatic diisocyanates includeisophorone diisocyanate (IPDI), cyclohexane diisocyanate,methylcyclohexane diisocyanate, bis(isocyanatomethyl)cyclohexane,bis(isocyanatocyclohexyl)methane, bis(isocyanatocyclohexyl)-2,2-propane,bis(isocyanatocyclohexyl)-1,2-ethane,2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2.2.1]-heptane,2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2.2.1]-heptane,2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2.2.1]-heptane,2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2.2.1]-heptane,2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2.2.1]-heptane,2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanatoethyl)-bicyclo[2.2.1]-heptane,and2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2.2.1]-heptane.

Examples of suitable aromatic diisocyanates in which the isocyanategroups are not bonded directly to the aromatic ring includebis(isocyanatoethyl)benzene, α, α, α′, α′-tetramethylxylenediisocyanate, 1,3-bis(1-isocyanato-1-methylethyl)benzene,bis(isocyanatobutyl)benzene, bis(isocyanatomethyl)naphthalene,bis(isocyanatomethyl)diphenyl ether, bis(isocyanatoethyl)phthalate, and2,5-di(isocyanatomethyl)furan. Aromatic diisocyanates having isocyanategroups bonded directly to the aromatic ring include phenylenediisocyanate, ethylphenylene diisocyanate, isopropylphenylenediisocyanate, dimethylphenylene diisocyanate, diethylphenylenediisocyanate, diisopropylphenylene diisocyanate, naphthalenediisocyanate, methylnaphthalene diisocyanate, biphenyl diisocyanate,4,4′-diphenylmethane diisocyanate,bis(3-methyl-4-isocyanatophenyl)methane, bis(isocyanatophenyl)ethylene,3,3′-dimethoxy-biphenyl-4,4′-diisocyanate, diphenylether diisocyanate,bis(isocyanatophenylether)ethyleneglycol,bis(isocyanatophenylether)-1,3-propyleneglycol, benzophenonediisocyanate, carbazole diisocyanate, ethylcarbazole diisocyanate,dichlorocarbazole diisocyanate, 4,4′-diphenylmethane diisocyanate,p-phenylene diisocyanate, 2,4-toluene diisocyanate, and 2,6-toluenediisocyanate.

Additional examples of suitable aromatic diisocyanates include1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,6-toluenediisocyanate (2,6-TDI), 2,4-toluene diisocyanate (2,4-TDI), a blend of2,4-TDI and 2,6-TDI, 1,5-diisocyanato naphthalene, diphenyl oxide4,4′-diisocyanate, 4,4′-methylenediphenyl diisocyanate (4,4-MDI),2,4′-methylenediphenyl diisocyanate (2,4-MDI),2,2′-diisocyanatodiphenylmethane (2,2-MDI), diphenylmethane diisocyanate(MDI), 3,3′-dimethyl-4,4′-biphenylene isocyanate,3,3′-dimethoxy-4,4′-biphenylene diisocyanate,1-[(2,4-diisocyanatophenyl)methyl]-3-isocyanato-2-methyl benzene, and2,4,6-triisopropyl-m-phenylene diisocyanate.

Other examples of suitable diisocyanates include 1,3-phenylenediisocyanate, 1,4-phenylene diisocyanate, 2,6-toluene diisocyanate(2,6-TDI), 2,4-toluene diisocyanate (2,4-TDI), a blend of 2,4-TDI and2,6-TDI, 1,5-diisocyanato naphthalene, diphenyl oxide 4,4′-diisocyanate,4,4′-methylenediphenyl diisocyanate (4,4-MDI), 2,4′-methylenediphenyldiisocyanate (2,4-MDI), 2,2′-diisocyanatodiphenylmethane (2,2-MDI),diphenylmethane diisocyanate (MDI), 3,3′-dimethyl-4,4′-biphenyleneisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate,1-[(2,4-diisocyanatophenyl)methyl]-3-isocyanato-2-methyl benzene,2,4,6-triisopropyl-m-phenylene diisocyanate, 4,4-methylene dicyclohexyldiisocyanate (H12MDI), and a combination of any of the foregoing.

A diisocyanate can have the structure of Formula (8):

O═C═N—R⁵—N═C═O  (8)

where R⁵ represents a core of the diisocyanate such as a core of analiphatic diisocyanate or an aromatic diisocyanate.

Urethane-extended polythiol adducts can be prepared by reacting adiisocyanate and an un-extended polythiol adduct in the presence of acatalyst such as dibutyl tin dilaurate at high temperature. Aurethane-extended polythiol adduct can be solid at room temperature andcan be soluble in suitable solvents.

Terminal Modified Polythiol Adducts

Polythiol adducts provided by the present disclosure such as un-extendedpolythiol adducts of Formula (6) and urethane-extended polythiol adductsof Formula (7) may be modified for use with other chemistries. Terminalmodified adducts may comprise terminal epoxy groups, Michael acceptorgroups, isocyanate groups, alkenyl groups, hydroxyl groups,polyalkoxysilyl groups.

Isocyanate-Terminated Urethane-Containing Prepolymers

Isocyanate-terminated urethane-containing prepolymers provided by thepresent disclosure can comprise the reaction product of reactantscomprising a polythiol adduct such as a polythiol adduct such as anun-extended polythiol adduct or a urethane-extended polythiol adductprovided by the present disclosure; a thiol-terminated sulfur-containingprepolymer; and a diisocyanate.

A polythiol adduct can comprise any of those disclosed herein, includingpolythiol adducts of Formula (4), Formula (4a), Formula (4b), Formula(5), Formula (5a), Formula (5b), Formula (6), or a combination of any ofthe foregoing.

A diisocyanate used to prepare an isocyanate-terminatedurethane-containing prepolymer can include any suitable diisocyanatesuch as any of the diisocyanates disclosed herein, including aliphaticdiisocyanates and aromatic diisocyanates.

Thiol-terminated sulfur-containing prepolymers can includethiol-terminated polythioethers, thiol-terminated polysulfides,thiol-terminated sulfur-containing polyformals, or combinations of anyof the foregoing. A thiol-terminated sulfur-containing prepolymer can bedifunctional, trifunctional, or may have a functionality greater than 3such as from 4 to 6. A thiol-terminated sulfur-containing prepolymer caninclude a combination of thiol-terminated sulfur-containing prepolymershaving different functionalities such that an average functionality ofthe thiol-terminated sulfur-containing prepolymer is a non-integervalue. For example, the average functionality of a thiol-terminatedsulfur-containing prepolymer can be from 2.05 to 2.9, from 2.05 to 2.8from 2.1 to 2.6, or from 2.1 to 2.4.

A thiol-terminated sulfur-containing prepolymer can comprise athiol-terminated sulfur-containing prepolymer of Formula (9a), athiol-terminated sulfur-containing prepolymer of Formula (9b), athiol-terminated sulfur-containing prepolymer of Formula (9c), or acombination of any of the foregoing:

HS—P—SH  (9a)

{HS—P—S—V′—}_(z)B  (9b)

{HS—(—R⁶—S—S—)_(a)—CH₂—}₂CH—(—S—S—R⁶—)_(a)—SH  (9c)

wherein,

-   -   each P independently comprises a polythioether moiety or a        polysulfide moiety;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol;    -   each —V′— is derived from the reaction of —V with a thiol;    -   each a is independently an integer from 1 to 50;    -   the sum of each a is an integer from 3 to 60; and    -   each R⁶ comprises a moiety having the structure        —(CH₂)₂—O—CH₂—O—(CH₂)₂—.

In prepolymers of Formula (9a) and Formula (9b), P can comprise a coreor backbone of a polythioether prepolymer or a core or backbone of apolysulfide prepolymer. In prepolymers of Formula (9a) and Formula (9b),P can comprise one or more thioether groups —S— and/or one or more ethergroups —O—.

Polythioether Prepolymers

A thiol-terminated sulfur-containing prepolymer can comprise athiol-terminated polythioether prepolymer comprising a backbonecomprising the structure of Formula (10):

—R¹—[—S—(CH₂)₂—O—[—R²—O—]_(m)—(CH₂)₂—S—R¹—S—]_(n)—  (10)

wherein,

-   -   each R¹ is independently selected from a C₂₋₁₀ n-alkanediyl        group, a C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl        group, a C₆₋₁₀ alkanecycloalkanediyl group, a heterocyclic        group, a —[(—CHR³—)_(p)—X—]_(q)—(CHR³)_(r)— group, wherein each        R³ is selected from hydrogen and methyl;    -   each R² is independently selected from a C₂₋₁₀ n-alkanediyl        group, a C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl        group, a C₆₋₁₄ alkanecycloalkanediyl group, a heterocyclic        group, and a —[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)— group;    -   each X is independently selected from O, S, —NH—, and —N(—CH₃)—;    -   m is an integer from 0 to 50;    -   n is an integer ranging from 1 to 60;    -   p is an integer ranging from 2 to 6;    -   q is an integer ranging from 1 to 5; and    -   r is an integer ranging from 2 to 10.

For example, P in thiol-terminated sulfur-containing prepolymers ofFormula (9a) and Formula (9b) can have the structure of Formula (10).

A thiol-terminated polythioether prepolymer can comprise athiol-terminated polythioether prepolymer of Formula (11a), athiol-terminated polythioether prepolymer of Formula (11b), or acombination thereof:

HS—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—SH  (11a)

{HS—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—V′—}_(z)B  (11b)

wherein,

-   -   each R¹ is independently selected from C₂₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, C₅₋₈        heterocycloalkanediyl, and —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—,        wherein,        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5;        -   r is an integer from 2 to 10;        -   each R³ is independently selected from hydrogen and methyl;            and    -   each X is independently selected from —O—, —S—, —NH—, and        —N(—CH₃)—;    -   each R² is independently selected from C₁₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, and        —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³, and X        are as defined as for R¹;    -   m is an integer from 0 to 50;    -   n is an integer from 1 to 60;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol; and        -   each —V′— is derived from the reaction of —V with a thiol.

In thiol-terminated polythioethers of Formula (11a) and in Formula(11b), R¹ can be —[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)—, where p can be 2, Xcan be —O—, q can be 2, r can be 2, R² can be ethanediyl, m can be 2,and n can be 9.

In thiol-terminated polythioethers of Formula (11a) and Formula (11b),R¹ can be C₂₋₆ alkanediyl or —[—(CHR³)_(s)—X—]_(q)—(CHR³)_(r)—.

In thiol-terminated polythioethers of Formula (11a) and Formula (11b),R¹ can be —[—(CHR³)_(s)—X—]_(q)—(CHR³)_(r)—, or X can be —O—, or X canbe —S—.

In thiol-terminated polythioethers of Formula (11a) and Formula (11b),R¹ can be —[—(CHR³)_(s)—X—]_(q)—(CHR³)_(r)—, p can be 2, r can be 2, qcan be 1, and X can be —S—; or, p can be 2, q can be 2, r can be 2, andX can be —O—; or p can be 2, r can be 2, q can be 1, and X can be —O—.

In thiol-terminated polythioether prepolymers of Formula (11a) andFormula (11b), R¹ can be —[—(CHR³)_(s)—X—]_(q)—(CHR³)_(r)—, each R³ canbe hydrogen, or at least one R³ is methyl.

In thiol-terminated polythioethers of Formula (11a) and Formula (11b),each R¹ can be the same or at least one R¹ can be different.

In thiol-terminated polythioether prepolymers of Formula (11a) andFormula (11b), m can be, for example, an integer from 0 to 50; from 0 to10, from 1 to 10, or from 2 to 10.

In thiol-terminated polythioether prepolymers of Formula (11a) andFormula (11b), n can be, for example, an integer from 1 to 60; from 1 to10, from 2 to 10, or from 3 to 10.

A thiol-terminated sulfur-containing prepolymer can comprise athiol-terminated polythioether prepolymer. Examples of thiol-functionalpolythioether prepolymers are disclosed, for example, in U.S. Pat. No.6,172,179, which is incorporated by reference in its entirety. Athiol-functional polythioether prepolymer can comprise Permapol® P3.1E,available from PRC-DeSoto International Inc., Sylmar, Calif.

A thiol-terminated polythioether prepolymer can have, for example, aweight average molecular weight from 1,000 Daltons to 10,000 Daltons,from 2,000 Daltons to 5,000 Daltons, or from 3,000 Daltons to 4,000Daltons. A thiol-terminated polythioether prepolymer can have an averagethiol functionality from 2.05 to 3.0, such as from 2.1 to 2.6.

A thiol-terminated polythioether prepolymer may comprise a mixture ofdifferent polythioethers and the polythioethers may have the same ordifferent functionality. A thiol-terminated polythioether prepolymer canhave an average functionality from 2 to 6, from 2 to 4, from 2 to 3, orfrom 2.05 to 2.5. For example, a thiol-terminated polythioetherprepolymer can comprise a difunctional sulfur-containing polymer, atrifunctional sulfur-containing polymer, or a combination thereof.

Various methods can be used to prepare thiol-terminated polythioethersof Formula (11 a) and Formula (11b). Examples of suitablethiol-terminated polythioethers, and methods for their production, aredescribed in U.S. Pat. No. 6,172,179, which is incorporated by referencein its entirety. Such thiol-terminated polythioethers may bedifunctional, that is, linear polymers having two terminal thiol groups,or polyfunctional, that is, branched polymers have three or moreterminal thiol groups.

A thiol-terminated polythioether can be prepared by reacting a polythioland a diene such as a divinyl ether, and the respective amounts of thereactants used to prepare the polythioethers can be chosen to yieldterminal thiol groups. Thus, in some cases, (n or >n, such as n+1) molesof a polythiol, such as a dithiol or a mixture of at least two differentdithiols and about 0.05 moles to 1 moles, such as 0.1 moles to 0.8moles, of a thiol-terminated polyfunctionalizing agent may be reactedwith (n) moles of a diene, such as a divinyl ether, or a mixture of atleast two different dienes, such as a combination of divinyl ether. Athiol-terminated polyfunctionalizing agent can be present in thereaction mixture in an amount sufficient to provide a thiol-terminatedpolythioether having an average functionality from 2.05 to 3, such as2.1 to 2.8.

A reaction used to make a thiol-terminated polythioether may becatalyzed by a free radical catalyst. Suitable free radical catalystsinclude azo compounds, for example azobisnitrile compounds such asazo(bis)isobutyronitrile (AIBN); organic peroxides, such as benzoylperoxide and tert-butyl peroxide; and inorganic peroxides, such ashydrogen peroxide. The reaction can also be effected by irradiation withultraviolet light either with or without a radicalinitiator/photosensitizer. Ionic catalysis methods, using eitherinorganic or organic bases, e.g., triethylamine, may also be used.

Suitable thiol-terminated polythioethers may be produced by reacting adivinyl ether or a mixture of divinyl ethers with a molar excess ofdithiol or a molar excess of a mixture of dithiols.

Thus, a thiol-terminated polythioether can comprise the reaction productof reactants comprising:

(a) a dithiol of Formula (12):

HS—R¹—SH  (12)

-   -   wherein,        -   R¹ is selected from C₂₋₆ alkanediyl, C₆₋₈ cycloalkanediyl,            C₆₋₁₀ alkanecycloalkanediyl, C₅₋₈ heterocycloalkanediyl, and            —[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—; wherein,            -   each R³ is independently selected from hydrogen and                methyl;            -   each X is independently selected from —O—, —S—, —NH—,                and —N(—CH₃)—;            -   p is an integer from 2 to 6;            -   q is an integer from 1 to 5; and            -   r is an integer from 2 to 10; and                (b) a divinyl ether of Formula (13):

CH₂═CH—O—(—R²—O—)_(m)—CH═CH₂  (13)

-   -   wherein,        -   each R² is independently selected from C₁₋₁₀ alkanediyl,            C₆₋₈ cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, and            —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³,            and X are as defined above; and        -   m is an integer from 0 to 50.

The reactants used to prepare a thiol-terminated polythioether may alsocomprise (c) a polyfunctional compound such as a polyfunctional compoundB(—V)_(z), where B, —V, and z are as defined herein.

Dithiols suitable for use in preparing thiol-terminated polythioethersinclude those having the structure of Formula (12), other dithiolsdisclosed herein, or combinations of any of the dithiols disclosedherein. For example, a dithiol has the structure of Formula (12):

HS—R¹—SH  (12)

wherein,

-   -   R¹ is selected from C₂₋₆ alkanediyl, C₆₋₈ cycloalkanediyl, C₆₋₁₀        alkanecycloalkanediyl, C₅₋₈ heterocycloalkanediyl, and        —[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—; wherein,        -   each R³ is independently selected from hydrogen and methyl;        -   each X is independently selected from —O—, —S—, and —NR—            wherein R is selected from hydrogen and methyl;        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5; and        -   r is an integer from 2 to 10.

In dithiols of Formula (12), R¹ can be—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—.

In dithiols of Formula (12), X can be —O— or —S—, and thus—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)— in Formula (12) can be—[(—CHR³—)_(p)—O—]_(q)—(CHR³)_(r)— or —[(—CHR³₂—)_(p)—S—]_(q)—(CHR³)_(r)—. P and r can be the same, such as where pand r are both two.

In dithiols of Formula (12), R¹ can be selected from C₂₋₆ alkanediyl and—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—.

In dithiols of Formula (12), R¹ can be—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—, and X can be —O—, or X can be —S—.

In dithiols of Formula (12), R¹ can be—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—, p can be 2, r can be 2, q can be 1,and X can be —S—; or p can be 2, q can be 2, r can be 2, and X can be—O—; or p can be 2, r can be 2, q can be 1, and X can be —O—.

In dithiols of Formula (12), R¹ can be—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—, each R³ can be hydrogen, or at leastone R³ can be methyl.

In dithiols of Formula (12), each R¹ can be derived fromdimercaptodioxaoctane (DMDO) or each R¹ can be derived fromdimercaptodiethylsulfide (DMDS).

In dithiols of Formula (12), each p can independently be selected from2, 3, 4, 5, and 6; or each p can be the same and can be 2, 3, 4, 5, or6.

In dithiols of Formula (12), each q can independently be selected from1, 2, 3, 4, and 5; or each q can be the same and can be 2, 3, 4, or 5.

In dithiols of Formula (12), each r can independently be selected from2, 3, 4, 5, 6, 7, 8, 9, or 10; or each r can be the same and can be 2,3, 4, 5, 6, 7, 8, 9, or 10.

Examples of suitable dithiols include 1,2-ethanedithiol,1,2-propanedithiol, 1,3-propanedithiol, 1,3-butanedithiol,1,4-butanedithiol, 2,3-butanedithiol, 1,3-pentanedithiol,1,5-pentanedithiol, 1,6-hexanedithiol, 1,3-dimercapto-3-methylbutane,dipentenedimercaptan, ethylcyclohexyldithiol (ECHDT),dimercaptodiethylsulfide, methyl-substituted dimercaptodiethylsulfide,dimethyl-substituted dimercaptodiethylsulfide, dimercaptodioxaoctane,1,5-dimercapto-3-oxapentane, and a combination of any of the foregoing.A dithiol may have one or more pendent groups selected from a lower(e.g., C₁₋₆) alkyl group, a lower alkoxy group, and a hydroxy group.Suitable alkyl pendent groups include, for example, C₁₋₆ linear alkyl,C₃₋₆ branched alkyl, cyclopentyl, and cyclohexyl.

Other examples of suitable dithiols include dimercaptodiethylsulfide(DMDS) (in Formula (12), R¹ is —[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)—, whereinp is 2, r is 2, q is 1, and X is —S—); dimercaptodioxaoctane (DMDO) (inFormula (12), R¹ is —[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)—, wherein p is 2, qis 2, r is 2, and X is —O—); and 1,5-dimercapto-3-oxapentane (in Formula(12), R¹ is —[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)—, wherein p is 2, r is 2, qis 1, and X is —O—). It is also possible to use dithiols that includeboth heteroatoms in the carbon backbone and pendent alkyl groups, suchas methyl groups. Such compounds include, for example,methyl-substituted DMDS, such as HS—CH₂CH(CH₃)—S—CH₂CH₂—SH,HS—CH(CH₃)CH₂—S—CH₂CH₂—SH and dimethyl-substituted DMDS, such asHS—CH₂CH(CH₃)—S—CHCH₃CH₂—SH and HS—CH(CH₃)CH₂—S—CH₂CH(CH₃)—SH.

Suitable divinyl ethers for preparing polythioethers include, forexample, divinyl ethers of Formula (13):

CH₂═CH—O—(—R²—O—)_(m)—CH═CH₂  (13)

where R² in Formula (13) is selected from a C₂₋₆ n-alkanediyl group, aC₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a C₆₋₁₀alkanecycloalkanediyl group, and —[(—CH₂—)_(p)—O—]_(q)—(—CH₂—)_(r)—,where p is an integer ranging from 2 to 6, q is an integer from 1 to 5,and r is an integer from 2 to 10. In a divinyl ether of Formula (13), R²can be a C₂₋₆ n-alkanediyl group, a C₃₋₆ branched alkanediyl group, aC₆₋₈ cycloalkanediyl group, a C₆₋₁₀ alkanecycloalkanediyl group, and inor —[(—CH₂—)_(p)—O—]_(q)—(—CH₂—)_(r)—.

In divinyl ethers of Formula (13), each m can independently be aninteger from 1 to 3, each m can be the same and can be 1, 2, or 3.

Suitable divinyl ethers include, for example, compounds having at leastone oxyalkanediyl group, such as from 1 to 4 oxyalkanediyl groups, i.e.,compounds in which m in Formula (13) is an integer ranging from 1 to 4.In divinyl ethers of Formula (13) m can be an integer ranging from 2 to4. It is also possible to employ commercially available divinyl ethermixtures that are characterized by a non-integral average value for thenumber of oxyalkanediyl units per molecule. Thus, m in Formula (13) canalso take on rational number values ranging from 0 to 10.0, such as from1.0 to 10.0, from 1.0 to 4.0, or from 2.0 to 4.0.

Examples of suitable divinyl ethers include, divinyl ether, ethyleneglycol divinyl ether (EG-DVE) (R² in Formula (13) is ethanediyl and m is1), butanediol divinyl ether (BD-DVE) (R² in Formula (13) is butanediyland m is 1), hexanediol divinyl ether (HD-DVE) (R² in Formula (13) ishexanediyl and m is 1), diethylene glycol divinyl ether (DEG-DVE) (R² inFormula (13) is ethanediyl and m is 2), triethylene glycol divinyl ether(R² in Formula (13) is ethanediyl and m is 3), tetraethylene glycoldivinyl ether (R² in Formula (13) is ethanediyl and m is 4),cyclohexanedimethanol divinyl ether, polytetrahydrofuryl divinyl ether;trivinyl ether monomers, such as trimethylolpropane trivinyl ether;tetrafunctional ether monomers, such as pentaerythritol tetravinylether; and combinations of two or more such polyvinyl ether monomers. Apolyvinyl ether may have one or more pendent groups selected from alkylgroups, hydroxy groups, alkoxy groups, and amine groups.

Divinyl ethers in which R² in Formula (13) is C₃₋₆ branched alkanediylmay be prepared by reacting a polyhydroxy compound with acetylene.Examples of divinyl ethers of this type include compounds in which R² inFormula (13) is an alkyl-substituted methanediyl group such as—CH(—CH₃)—, for which R² in Formula (13) is ethanediyl and m is 3.8 oran alkyl-substituted ethanediyl.

Other useful divinyl ethers include compounds in which R² in Formula(13) is polytetrahydrofuryl (poly-THF) or polyoxyalkanediyl, such asthose having an average of about 3 monomer units.

Two or more types of divinyl ether monomers of Formula (13) may be used.Thus, two dithiols of Formula (12) and one divinyl ether monomer ofFormula (13), one dithiol of Formula (12) and two divinyl ether monomersof Formula (13), two dithiols of Formula (12) and two divinyl ethermonomers of Formula (13), and more than two compounds of one or bothFormula (12) and Formula (13), may be used to produce a variety ofthiol-terminated polythioethers.

A divinyl ether monomer can comprise 20 to less than 50 mole percent ofthe reactants used to prepare a thiol-terminated polythioether, or 30mole percent to less than 50 mole percent.

Relative amounts of dithiols and divinyl ethers can be selected to yieldpolythioethers having terminal thiol groups. Thus, a dithiol of Formula(12) or a mixture of at least two different dithiols of Formula (12),can be reacted with of a divinyl ether of Formula (13) or a mixture ofat least two different divinyl ethers of Formula (13) in relativeamounts such that the molar ratio of thiol groups to alkenyl groups isgreater than 1:1, such as from 1.1 to 2.0:1.0.

The reaction between dithiols and divinyl ethers and/or polythiols andpolyvinyl ethers may be catalyzed by a free radical catalyst. Suitablefree radical catalysts include, for example, azo compounds, for exampleazobisnitriles such as azo(bis)isobutyronitrile (AIBN); organicperoxides such as benzoyl peroxide and t-butyl peroxide; and inorganicperoxides such as hydrogen peroxide. The catalyst may be a free-radicalcatalyst, an ionic catalyst, or ultraviolet radiation. A catalyst doesnot comprise acidic or basic compounds, and does not produce acidic orbasic compounds upon decomposition. Examples of free-radical catalystsinclude azo-type catalyst, such as Vazo®-57 (Du Pont), Vazo®-64 (DuPont), Vazo®-67 (Du Pont), V-70® (Wako Specialty Chemicals), and V-65B®(Wako Specialty Chemicals). Examples of other free-radical catalystsinclude alkyl peroxides, such as t-butyl peroxide. The reaction may alsobe effected by irradiation with ultraviolet light either with or withouta cationic photoinitiating moiety.

Thiol-terminated polythioethers provided by the present disclosure maybe prepared by combining at least one dithiol of Formula (12) and atleast one divinyl ether of Formula (13) followed by addition of anappropriate catalyst, and carrying out the reaction at a temperaturefrom 30° C. to 120° C., such as 70° C. to 90° C., for a time from 2hours to 24 hours, such as 2 hours to 6 hours.

Thiol-terminated polythioethers may comprise a polyfunctionalpolythioether, i.e., may have an average functionality of greater than2.0. Suitable polyfunctional thiol-terminated polythioethers include,for example, those having the structure of Formula (11b):

{HS—R¹—[—S—(CH₂)_(p)—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—V′—}_(z)B  (11b)

wherein z has an average value of greater than 2.0, a value between 2and 3, a value between 2 and 4, a value between 3 and 6, or an integerfrom 3 to 6.

Polyfunctionalizing agents suitable for use in preparing suchpolyfunctional thiol-terminated polymers include trifunctionalizingagents, that is, compounds where z is 3. Suitable trifunctionalizingagents include, for example, triallyl cyanurate (TAC),1,2,3-propanetrithiol, isocyanurate-containing trithiols, andcombinations thereof, as disclosed in U.S. Application Publication No.2010/0010133 and in U.S. Application Publication No. 2011/0319559, eachof which is incorporated by reference in its entirety. Other usefulpolyfunctionalizing agents include trimethylolpropane trivinyl ether,and the polythiols described in U.S. Pat. Nos. 4,366,307; 4,609,762; and5,225,472, each of which is incorporated by reference in its entirety.Mixtures of polyfunctionalizing agents may also be used. As a result,polythioethers provided by the present disclosure may have a wide rangeof average functionality. For example, trifunctionalizing agents mayafford average functionalities from 2.05 to 3.0, such as from 2.1 to2.6. Wider ranges of average functionality may be achieved by usingtetrafunctional or higher functionality polyfunctionalizing agents.Functionality may also be determined by factors such as stoichiometry,as will be understood by those skilled in the art.

A polythioether prepolymer can have, for example, from 8 to 200—(CH₂)₂—S—(CH₂)₂— linkages. A thiol-terminated polythioether prepolymercan have an average molecular weight from 1,000 Daltons to 10,000Daltons, from 2,000 Daltons to 5,000 Daltons, or from 3,000 Daltons to4,000 Daltons. A thiol-terminated polythioether prepolymer can have anaverage functionality, for example, from 2.05 to 3.0 or from 2.1 to 2.6.

Thiol-Terminated Polysulfides

A thiol-terminated sulfur-containing prepolymer can comprise athiol-terminated polysulfide.

A polysulfide refers to a prepolymer that contains one or more sulfidelinkages, i.e., —S_(x)— linkages, where x can be, for example, from 2 to4, or from 2 to 6, in the polymer backbone and/or in pendent positionson the polymer chain. A polysulfide prepolymer can have two or moresulfur-sulfur linkages, such as —S—S—. Suitable thiol-terminatedpolysulfides are commercially available, for example, from Akzo Nobeland Toray Fine Chemicals under the names Thiokol®-LP and Thioplast®,respectively. Thioplast® products are available in a wide range ofmolecular weights ranging, for example, from less than 1,100 to over8,000, with molecular weight being the average molecular weight in gramsper mole. In some cases, a thiol-terminated polysulfide has a numberaverage molecular weight of 1,000 Daltons to 4,000 Daltons. Athiol-terminated polysulfide prepolymer can comprise a Thiokol-LP®polysulfide, a Thioplast® polysulfide, or a combination thereof. Thecrosslink density of these products can also vary, depending on theamount of crosslinking agent used. The —SH content, i.e., thiol ormercaptan content, of these products can also vary. The mercaptancontent and molecular weight of a polysulfide can affect the cure speedof the prepolymer, with cure speed increasing with molecular weight.Examples of suitable thiol-terminated polysulfide prepolymers aredisclosed, for example, in U.S. Pat. Nos. 4,623,711, 6,172,179,6,509,418, 7,009,032, and 7,879,955, each of which is incorporated byreference in its entirety.

Thioplast® polysulfides result from the poly-condensation ofbis-(2-chloroethyl-)formal with alkali polysulfide. This reactiongenerates long-chain macromolecules which can then be cleaved to arequired chain length by reductive splitting with sodium dithionate. Thedisulfide groups are at the same time converted into reactive thiolterminal groups. By introducing a trifunctional component such as1,2,3-trichloropropane during the synthesis, a third thiol terminalgroup can be added to a specific number of Thioplast® molecules toestablish the extent of cross-linking during the curing process. Thevalue for n may vary, for example, between 7 and 38 depending on theamount of the cleaving agent used. For certain applications, chainlength and branching will have to be varied.

A thiol-terminated polysulfide prepolymer can have an average thiolfunctionality, for example, from 2.1 to 2.5 or from 2.01 to 2.1. Athiol-terminated polysulfide prepolymer can have a weight averagemolecular weight from 1,000 Daltons to 8,000 Daltons, or from 1,000Daltons to 5,000 Daltons, an can have a low degree of branching. Athiol-terminated polysulfide prepolymer can have a degree of branching,for example, from 0 to 4, from 0 to 3, from 0 to 2.5, or from 0 to 2.0,where the degree of branching is expressed as mole percent of branchingwith respect to the prepolymer backbone.

A thiol-terminated sulfur-containing prepolymer can comprise, forexample, a thiol-terminated polysulfide having the structure of Formula(9c):

{HS—(—R⁶—S—S—)_(a)—CH₂—}₂CH—(—S—S—R⁶—)_(a)—SH  (9c)

wherein,

-   -   each a is independently an integer from 1 to 50;    -   the sum of each a is an integer from 5 to 60; and    -   each R⁶ comprises a moiety having the structure        —(CH₂)₂—O—CH₂—O—(CH₂)₂—

In thiol-terminated polysulfides of Formula (9c), each a can be aninteger from 1 to 50, such as from 5 to 35, from 5 to 20, or from 1 to10. In thiol-terminated polysulfides of Formula (9c), the sum of eachcan, for example, be from 5 to 60, from 10 to 40, or from 13 to 38. Forexample, in thiol-terminated polysulfides of Formula (9c), each a can be6 (Thiokol® LP-3) or each a can be 23 (Thiokol® LP-23).

A thiol-terminated polysulfide prepolymer can be difunctional,trifunctional, have a higher functionality than three, or may be acombination of different functionalities. A thiol-terminated polysulfideprepolymer can be a trifunctional thiol-terminated polysulfide,including a mixture of trifunctional thiol-terminated polysulfides.

A thiol-terminated polysulfide can comprise, for example, Thiokol® LP-3,Thiokol® LP-32, or a combination thereof. A thiol-terminated polysulfidecan have a mole percent (%) thiol content from 1 to 7, an averagemolecular weight from 1,100 Daltons to 6,500 Daltons, a mole percent (%)sulfur content of 37 to 38, and from 0.2 mol % to 2 mol % of apolyfunctionalizing agent

A thiol-terminated polysulfide can comprise bis(ethyleneoxy)methanecontaining disulfide linkages.

A thiol-terminated polysulfide can have an average thiol functionalityfrom 2 to 2.5, from 2 to 2.4, from 2 to 2.3, from 2 to 2.2, or from 2 to2.1. A thiol-terminated polysulfide can have an average molecular weightfrom 1,000 Daltons to 8,000 Daltons, from 1,000 Daltons to 6,000Daltons, from 1,000 Daltons to 5,000 Daltons, or from 1,000 to 3,000Daltons. Thiol-terminated polysulfides can be characterized by anaverage low degree of branching such as from 0 to 4, from 0 to 3, from 0to 2.5, or from 0 to 2.0, where the degree of branching is expressed asmole percent of branches per mole of polysulfide backbone.

Thiol-Terminated Sulfur-Containing Polyformals

Sulfur-containing polyformal prepolymers useful in aerospace sealantapplications are disclosed, for example, in U.S. Application PublicationNo. 2012/0234205 and in U.S. Application Publication No. 2012/0238707,each of which is incorporated by reference in its entirety.

Isocyanate-Terminated Urethane-Containing Prepolymers

Isocyanate-terminated urethane-containing prepolymers can comprise thereaction product of reactants comprising a thiol-terminatedsulfur-containing prepolymer, a polythiol adduct, and a diisocyanate.

In general it is desirable that isocyanate-terminatedurethane-containing prepolymers provided by the present disclosure havea low viscosity such as less than 10 Poise, less than 25 Poise, lessthan 50 Poise, or less than 100 Poise. The use of low viscosityprepolymers facilitates the use of less solvent in a composition. Forexample, it can be desirable that a composition contain less than 5 wt %solvent or less than 10 wt % solvent. The use of low solvent content canlead to less shrinkage of an applied coating. Isocyanate-terminatedurethane-containing prepolymers provided by the present disclosure canalso have a viscosity greater than 100 Poise, such as, for example, from100 Poise to 500 Poise.

A thiol-terminated sulfur-containing prepolymers can comprise athiol-terminated polythioether, a thiol-terminated polysulfide, athiol-terminated sulfur-containing polyformal, or a combination of anyof the foregoing. A polythiol adduct can comprise an un-extendedpolythiol adduct, a urethane-extended polythiol adduct, or a combinationthereof. A diisocyanate can include an aliphatic diisocyanate, anaromatic diisocyanate, or a combination thereof, including any of thediisocyanates disclosed herein.

An isocyanate-terminated urethane-containing prepolymer can comprise anisocyanate-terminated urethane-containing prepolymer of Formula (15a),an isocyanate-terminated urethane-containing prepolymer of Formula(15b), or a combination thereof:

D-S—P—S-D  (15a)

{D-S—P—S—V′—}_(z)B   (15b)

wherein,

-   -   each D independently can comprise a moiety having the structure        of Formula (16a), Formula (16b), Formula (16c), Formula (16d),        Formula (16e), Formula (16f), or Formula (16g):

—C(═O)—NH—R⁵—N═C═O  (16a)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O  (16b)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—N═C═O}_(z-1)  (16c)

—C(═O)—NH—R⁵—{—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—}_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16d)

—C(═O)—NH—R⁵—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—N═C═O}_(z-1)  (16e)

—C(═O)—NH—R⁵—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16f)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S—P—S—V′—B{—V′—S—P—S—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O}_(z-1)  (16g)

wherein,

-   -   each R⁵ independently comprises a core of a diisocyanate;    -   each m is an integer from 1 to 10;    -   each E comprises a core of a polythiol adduct;    -   each P comprises a polythioether moiety or a polysulfide moiety;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol; and    -   each —V′— is derived from the reaction of —V with a thiol.

In isocyanate-terminated urethane-containing prepolymers of Formula(15a) and Formula (15b), each E can independently comprise a moietyhaving the structure of Formula (6a) or Formula (7a):

—(—R¹—S—R²—S—)_(n)—R¹—  (6a)

-(-A-S—C(═O)—NH—R⁵—NH—C(═O)—S—)_(m)-A-   (7a)

wherein,

-   -   each A independently comprises a moiety having the structure of        Formula (6a);    -   n is an integer from 1 to 10;        -   each R¹ independently comprises a structure of Formula (1a):

—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a)

-   -   -   wherein,            -   each R³ is independently selected from hydrogen and                methyl;            -   each X is independently selected from O and S;            -   p is an integer from 2 to 6;            -   q is an integer from 1 to 5; and            -   r is an integer from 2 to 10;

    -   each R² independently comprises a moiety having the structure of        Formula (3a):

—C(—R⁴)₂—  (3a)

-   -   -   where each R⁴ independently comprises C₁₋₅ alkyl; and

    -   each R⁵ is a core of a diisocyanate.

In isocyanate-terminated urethane-containing prepolymers of Formula(15a) and Formula (15b), each P can comprise a moiety of Formula (11c)or a moiety of Formula (18):

—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—  (11c)

—(CH₂)₂—O—CH₂—O—(CH₂)₂—  (18)

where m, n, R¹ and R² are defined as for Formula (11a).

An isocyanate-terminated urethane-containing prepolymer can have thestructure of the Formula (19):

{D-S—}₃G  (19)

wherein,

-   -   G is a moiety of Formula (9d):

{—(—R⁶—S—S—)_(a)—CH₂—}₂CH—(—S—S—R⁶—)_(a)—  (9d)

-   -   -   wherein,            -   each a is independently an integer from 1 to 50;            -   the sum of each a is an integer from 5 to 60; and            -   each R⁶ comprises a moiety having the structure                —(CH₂)₂—O—CH₂O—(CH₂)₂—; and

    -   each D independently can comprise a moiety having the structure        of Formula (20a), Formula (20b), Formula (20c) or Formula (20d)

—C(═O)—NH—R⁵—N═C═O  (20a)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O  (20b)

—C(═O)—NH—R⁵—NH—C(═O)—S-G{-S-D′}₂   (20c)

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—NH—C(═O)—S-G{-S-D′}₂  (20d)

wherein,

-   -   each R⁵ independently comprises a core of a diisocyanate;    -   each m is an integer from 1 to 10;    -   each E comprises a core of a polythiol adduct; and    -   each D′ comprises a moiety of Formula (20a) or a moiety of        Formula (20b).

In the polyaddition reaction between a thiol-terminatedsulfur-containing prepolymer, a polythiol adduct and a diisocyanate, thereactants can comprise an equivalent ratio of thiol-terminatedsulfur-containing prepolymer from about 2:5 to about 1.5:4, from about1:3 to about 1:5, or about 1:3. The total diisocyanate equivalent tothiol equivalent index can be from about 2.0 to about 2.1, and theequivalent ratio of diisocyanate to thiol can be from about 5:1 to about2:1. The equivalent ratio can also be selected to provide aurethane-containing prepolymer comprising terminal thiol groups. Theequivalent ratio can also be selected to provide a urethane-containingprepolymer comprising terminal isocyanate groups.

An isocyanate-terminated urethane-containing prepolymer provided by thepresent disclosure can also comprise the reaction product of reactantscomprising an isocyanate-terminated sulfur-containing prepolymer, apolythiol adduct, and a diisocyanate; where the isocyanate-terminatedsulfur-containing prepolymer can comprise the reaction product ofreactants comprising a diisocyanate and a thiol-terminatedsulfur-containing prepolymer.

For example, a thiol-terminated polysulfide or combination ofthiol-terminated polysulfides can be reacted with a diisocyanate such asan aliphatic diisocyanate or an aromatic diisocyanate to provide anisocyanate-terminated polysulfide. An isocyanate-terminated polysulfidemay first be prepared and then combined with a polythiol adduct providedby the present disclosure and a diisocyanate to provide anisocyanate-terminated urethane-containing prepolymer.

Examples of suitable isocyanate-terminated polysulfides include thosederived from Thiokol®-LP polysulfides, which can compriseisocyanate-terminated polysulfides having the structure of Formula (20):

{O═C═N—R⁵—NH—C(═O)—S—[—(CH₂)₂—O—CH₂—O—(CH₂)₂—S—S—]_(a)—(CH₂)₂—}₂CH—[—S—S—O—CH₂—O—(CH₂)₂—]_(n)—S—C(═O)—NH—R⁵—N═C═O  (20)

where each R⁵ comprises a core of a diisocyanate such as a core of analiphatic or an aromatic diisocyanate, and n can be an integer from 1 to50, such as from 5 to 35.

For example, in isocyanate-terminated polysulfides of Formula (20), ncan be 6 (Thiokol® LP-3) or n can be 23 (Thiokol® LP-23). In addition toisocyanate-terminated polysulfides of Formula (20),isocyanate-terminated polysulfides can comprise isocyanate-terminatedpolysulfides in which two or more polyfunctional polysulfides are bondedtogether via a diisocyanate.

An isocyanate-terminated urethane-containing polysulfide can be preparedby reacting a thiol-terminated polysulfide and a diisocyanate in thepresence of a tin catalyst.

An isocyanate-terminated sulfur-containing prepolymer can comprise anisocyanate-terminated polythioether of Formula (21a), anisocyanate-terminated polythioether of Formula (21b), or a combinationthereof:

R⁶—S—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—R⁶  (21a)

{R⁶—S—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—V′—}_(z)B  (21b)

wherein,

-   -   each R¹ independently is selected from C₂₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, C₅₋₈        heterocycloalkanediyl, and —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—,        wherein,        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5;        -   r is an integer from 2 to 10;        -   each R³ is independently selected from hydrogen and methyl;            and        -   each X is independently selected from —O—, —S—, —NH—, and            —N(—CH₃)—;        -   each R² is independently selected from C₁₋₁₀ alkanediyl,            C₆₋₈ cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, and            —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³,            and X are as defined as for R¹;        -   m is an integer from 0 to 50;        -   n is an integer from 1 to 60;        -   B represents a core of a z-valent, polyfunctionalizing agent            B(—V)_(z) wherein,            -   z is an integer from 3 to 6; and            -   each V is a moiety comprising a terminal group reactive                with a thiol; and        -   each —V′— is derived from the reaction of —V with a thiol;            and    -   each R⁶ independently comprises a moiety having the structure of        Formula (22):

—C(═O)—NH—R⁵—N═C═O  (22)

-   -   -   wherein R⁵ comprises a core of a diisocyanate.

An isocyanate-terminated polythioether prepolymer of Formula (11a),Formula (11b), or a combination thereof, can be reacted with adiisocyanate and a polythiol adduct. These reactants can provide, forexample, isocyanate-terminated urethane-containing polythioethers ofFormula (23a) and Formula (23b):

R⁷—S—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—R⁷  (23a)

{R⁷—S—R¹—[—S—(CH₂)₂—O—(R²—O)_(m)—(CH₂)₂—S—R¹—]_(n)—S—V′—}_(z)B  (23b)

wherein,

-   -   each R⁷ can independently be a moiety of Formula (24):

—C(═O)—NH—R⁵—[—NH—C(═O)—S-E-S—C(═O)—NH—R⁵—]_(m)—N═C═O  (24)

-   -   wherein,        -   each E independently can comprise a moiety having the            structure of Formula (6a) or Formula (7a):

—(—R¹—S—R²—S—)_(n)—R¹—  (6a)

-(-A-S—C(═O)—NH—R⁵—NH—C(═O)—S—)_(m)-A-  (7a)

-   -   where n, m, z, R¹, R², R⁵, and R⁷ are defined as in Formula (6)        and Formula (7), and A is a moiety of Formula (7a).

An isocyanate-terminated sulfur-containing prepolymer can comprise anisocyanate-terminated polysulfide having the structure of Formula (25):

{R⁶—S—(—R⁸—S—S—)_(a)—CH₂—}₂CH—(—S—S—R⁸—)_(a)—S—R⁶  (25)

wherein,

-   -   each a can independently be an integer from 1 to 60;    -   the sum of each a can be an integer from 3 to 60;    -   each R⁵ comprises a moiety having the structure        —(CH₂)₂—O—CH₂—O—(CH₂)₂—; and    -   each R⁶ independently comprises a moiety having the structure of        Formula (22):

—C(═O)—NH—R⁵—N═C═O  (22)

-   -   -   where R⁵ comprises the core of a diisocyanate.

Monomeric Polythiols

In addition to a thiol-terminated sulfur-containing prepolymer, thereactants used to from an isocyanate-terminated urethane-containingprepolymer provided by the present disclosure can include a monomericpolythiol. Monomeric polythiols include low molecular weight polythiolsand can be used to control the hard segment and soft segment content ofthe polymer chain. Suitable monomeric polythiols include, for example,pentaerytrhitol tetra(3-mercaptopropionate),trimethylpropane-tri(3-mercaptopropionate),glycol-di(3-mercaptopropionate) or propyleneglycol(3-mercaptopropionate). Suitable monomeric polythiols and theiruse in polyurethane compositions are disclosed, for example, inInternational Publication No. WO 2009/095739, which is incorporated byreference in its entirety.

Compositions

Compositions can comprise an isocyanate-terminated urethane-containingprepolymer provided by the present disclosure. A composition can furthercomprise a curing agent such as a polyamine, a catalyst, a filler suchas a low density filler, adhesion promoters, pigments, other additives,or combinations of any of the foregoing.

Compositions may also employ alternative curing chemistries. Forexample, a composition may employ an epoxy/amine curing chemistry. Insuch compositions an isocyanate-terminated urethane-containingprepolymer may be modified to comprise terminal epoxy group by reactingan isocyanate-terminated urethane-containing prepolymer with an epoxidealcohol such as 2,3-epoxy-1-propanol (glycidol) to provide anepoxy-terminated urethane-containing prepolymer. The epoxy-terminatedurethane-containing prepolymer may be combined with a polyamine curingagent.

Polyamine

Compositions provided by the present disclosure can include a curingagent such as a polyamine curing agent or a polyepoxide curing agent.

A polyamine curing agent can comprise a polyamine such as a diamine,triamine or combination thereof. A diamine can comprise a cycloaliphaticdiamine. A cycloaliphatic diamine can comprise, for example,N-isopropyl-2-((isopropylamino)ethyl)-3,5,5-trimethylcyclohexan-1-amine,4,4′-methylenebis(N-(sec-butyl)cyclohexan-1-amine), or a combination ofany of the foregoing.

A polyamine suitable for use in compositions provided by the presentdisclosure can include polyetheramines such as Jeffamine®polyetheramines (Huntsman). Suitable polyetheramines are also availablefrom BASF. Polyetheramines contain primary amino groups attached to theendo f a polyether backbone. The polyether backbone can be based onpropylene oxide, ethylene oxide, or a combination thereof.Polyetheramines can be used as curing agent in sealant compositions.

A suitable aliphatic diamine can comprise Jefflink® 754, Clearlink®1000, or a combination thereof.

Suitable aliphatic diamine curing agents can also include any of thosedisclosed in U.S. Pat. No. 6,403,752, such as diamines of Formula (8),Formula (9), Formula (10), Formula (11), and Formula (12):

where x is an integer from 2 to 20; each of R¹ and R² are independentlyC₁₋₂₀ alkyl; each of R⁵ and R⁶ are independently C₄₋₂₀ alkyl; and eachof R³ and R⁴ are hydrogen or C₁₋₂₀ alkyl.

Compositions provided by the present disclosure can comprise from 0.01wt % to 0.2 wt % such as from 0.03 wt % to 0.13 wt % of a polyamine or acombination of polyamine, where wt % is based on the total weight of thecurable composition.

In general, the use of lower molecular weight polyamine curing agentsproduces harder, less flexible cured sealants, and the use of highermolecular weight polyamine curing agents produces softer, more flexiblecured sealants.

Polyamines suitable for use in compositions provided by the presentdisclosure can be liquid at room temperature. It is desirable thatpolyamines have a low viscosity at room temperature to facilitate theability of a polyamine to coat or cover low density filler particles.

Low Density Filler

Compositions provided by the present disclosure can include a lowdensity filler.

Compositions provided by the present disclosure can have a specificgravity, for example, from 0.70 to 0.80, from 0.70 to 0.78, from 0.70 to0.76, from 0.70 to 0.74, or from 0.71 to 0.74.

Compositions and sealants provided by the present disclosure may includeone or more light weight, low density fillers. As used herein, lowdensity, when used with reference to such particles means that theparticles are characterized by a specific gravity of no more than 0.7,no more than 0.25, or no more than 0.1. Suitable lightweight fillerparticles often fall within two categories; microspheres and amorphousparticles. The specific gravity of microspheres may range from 0.1 to0.7 and include, for example, polystyrene foam, microspheres ofpolyacrylates and polyolefins, and silica microspheres having particlesizes ranging from 5 microns to 100 microns and a specific gravity of0.25 (Eccospheres®). Other examples include alumina/silica microsphereshaving particle sizes in the range of 5 microns to 300 microns and aspecific gravity of 0.7 (Fillite®), aluminum silicate microsphereshaving a specific gravity of from about 0.45 to about 0.7 (Z-Light®),calcium carbonate-coated polyvinylidene copolymer microspheres having aspecific gravity of 0.13 (Dualite® 6001AE), and calcium carbonate coatedacrylonitrile copolymer microspheres such as Dualite® E135, having anaverage particle size of about 40 μm and a density of 0.135 g/cm³(Henkel). Suitable fillers for decreasing the specific gravity of thecomposition include, for example, hollow microspheres such as Expancel®microspheres (available from AkzoNobel) or Dualite® low density polymermicrospheres (available from Henkel). Compositions provided by thepresent disclosure include lightweight filler particles comprising anexterior surface coated with a thin coating, such as those described inU.S. Application Publication No. 2010/0041839, which is incorporated byreference in its entirety.

A light weight filler can comprise Expancel® microspheres characterizedby a density of 25 kg/m³ or 60 kg/m³, and an average particle diameterfrom 20 μm to 120 μm. Expancel® microspheres can be provided in expandedform.

A low density filler can comprise less than 2 wt % of a composition,less than 1.5 wt %, less than 1.0 wt %, less than 0.8 wt %, less than0.75 wt %, less than 0.7 wt %, or less than 0.5 wt % of a composition,where wt % is based on the total dry solids weight of the composition.

A low density filler, also referred to as a light weight filler, refersto microspheres or particles having a density less than 100 kg/m³, lessthan 80 kg/m³, less than 60 kg/m³. less than 40 kg/m³, or less than 20kg/m³. For example, a light weight filler can have a density from 10kg/m³ to 100 kg/m³, from 10 kg/m³ to 80 kg/m³, from 10 kg/m³ to 60kg/m³, or from 10 kg/m³ to 40 kg/m³. The particles can have an averageparticle size ranging from, for example, 1 μm to 500 μm, from 5 μm to300 μm, from 10 μm to 200 μm, or from 20 μm to 100 μm.

A low density filler can comprise microspheres and/or nanospheres.

Compositions can comprise from 5 wt % to 40 wt %, from 5 wt % to 30 wt%, from 5 wt % to 20 wt %, from 5 wt % to 15 wt %, or from 10 wt % to 20wt % of a low density filler.

The addition of a low density filler to a composition can decrease theweight of the composition by 20% to 50%, such as from 30% to 40%,compared to the weight of the same volume of the composition without thelow density filler.

A low density filler can be mixed with the polyamine component toprovide polyamine-coated particles. The polyamine-coated low densityfiller can be combined with an isocyanate-terminated urethane-containingprepolymer to provide a curable composition.

Compositions provided by the present disclosure may also comprise, asthe low density filler, polyphenylene sulfide. Polyphenylene sulfide isa thermoplastic engineering resin that exhibits dimensional stability,chemical resistance, and resistance to corrosive and high temperatureenvironments. Polyphenylene sulfide engineering resins are commerciallyavailable, for example, under the tradenames Ryton® (Chevron), Techtron®(Quadrant), Fortron® (Celanese), and Torelina® (Toray). Polyphenylenesulfide resins are generally characterized by a density from about 1.3g/cc to about 1.4 g/cc, or about 1.35 g/cc. Low density polyphenylenesulfide filler, compositions comprising a polyphenylene sulfide filler,and uses thereof are disclosed in U.S. application Ser. No. 14/593,069filed on Jan. 9, 2015, entitled Low density fuel resistantsulfur-containing polymer compositions and uses thereof, which isincorporated by reference in its entirety.

For use in compositions provided by the present disclosure, apolyphenylene sulfide filler can be characterized by a particle size,for example, from 5 microns to 50 microns, from 5 microns to 75 microns,less than 75 microns, less than 50 microns, or less than 40 microns.

A polyphenylene sulfide filler can be obtained as pellets and thenground to a fine powder and filtered to obtain a desired nominalparticle size and/or desired particle size distribution.

Compositions provided by the present disclosure can comprise from about5 wt % to about 40 wt % of a polyphenylene sulfide filler, from 10 wt %to about 35 wt %, or from about 20 wt % to about 30 wt % of apolyphenylene sulfide filler, where wt % is based on the total weight ofthe composition when formulated as a coating or sealant.

A low density filler can be combined with a liquid polyamine curingagent and may include less than 10 wt %, less than 7 wt %, or less than5 wt % of a low boiling solvent such as ethyl acetate and/or butylacetate to provide a homogenous mixture in which the low density fillerparticles are covered with the polyamine curing agent. The mixture canbe dried to remove the solvent to provide a powder comprising lightweight filler particles coated a polyamine curing agent. Thepolyamine-coated light weight particles or microspheres can be combinedwith an isocyanate-terminated urethane-containing prepolymer provided bythe present disclosure to provide a curable composition.

Formulations

Compositions provided by the present disclosure may comprise one or moreadditional components suitable for use in aerospace sealants and dependat least in part on the desired performance characteristics of the curedsealant under conditions of use.

Sealants provided by the present disclosure can be suitable for as ClassA, Class B, or Class C aerospace sealants. A Class A sealant istypically applied by brushing and has a viscosity from about 150 Poiseto 500 Poise. A Class B sealant can be applied by extrusion such as byextrusion suing a pneumatic Semco® gun and is characterized by a highviscosity from about 8,000 Poise to about 16,000 Poise. A Class Bsealant can be used for forming fillets and sealing on vertical surfaceswhere low slump/sag is required. A Class C sealant can be applied usinga roller coating or a combed tooth spreader and has a medium viscosityfrom about 1,000 Poise to about 4,000 Poise. A Class C sealant is usedfor sealing fay surfaces.

Compositions provided by the present disclosure include curablecompositions and cured compositions. A curable composition comprises amixture of reactants that have not reacted or have partially reacted andwhere the viscosity of the curable composition is such that the curablecomposition can still be applied to a part for its intended purpose. Theviscosity at which the composition is no longer workable depends in parton the method of application such as whether the composition is applied,for example, by brushing, spraying, roller coating, pressing, orextrusion. A cured composition can refer to a composition in which thecomponents have reacted to an extent as to provide a tack-free surfaceand to provide a Shore A hardness of at least 30A.

Compositions provided by the present disclosure may include one or morecatalysts. A catalyst can be selected as appropriate for the curingchemistry employed. For example, when curing thiol-terminatedantioxidant-containing polythioether prepolymers and polyepoxides, thecatalyst can be an amine catalyst. A cure catalyst may be present in anamount from 0.1 to 5 weight percent, based on the total weight of thecomposition. Examples of suitable catalysts include1,4-diazabicyclo[2.2.2]octane (DABCO®, Air Products and DMP-30® (anaccelerant composition including 2,4,6-tris(dimethylaminomethyl)phenol).

Compositions provided by the present disclosure can comprise one or morethan one adhesion promoters. A one or more additional adhesion promotermay be present in amount from 0.1 wt % to 15 wt % of a composition, lessthan 5 wt %, less than 2 wt %, or, less than 1 wt %, based on the totaldry weight of the composition. Examples of adhesion promoters includephenolics, such as Methylon® phenolic resin, and organosilanes, such asepoxy, mercapto or amino functional silanes, such as Silquest® A-187 andSilquest® A-1100. Other useful adhesion promoters are known in the art.

Suitable adhesion promoters include sulfur-containing adhesion promoterssuch as those disclosed in U.S. Pat. No. 8,513,339, which isincorporated by reference.

Compositions provided by the present disclosure may comprise one or moredifferent types of filler. Suitable fillers include those commonly knownin the art, including inorganic fillers, such as carbon black andcalcium carbonate (CaCO₃), silica, polymer powders, and lightweightfillers. Suitable lightweight fillers include, for example, thosedescribed in U.S. Pat. No. 6,525,168. A composition can include 5 wt %to 60 wt % of the filler or combination of fillers, 10 wt % to 50 wt %,or from 20 wt % to 40 wt %, based on the total dry weight of thecomposition. Compositions provided by the present disclosure may furtherinclude one or more colorants, thixotropic agents, accelerators, fireretardants, adhesion promoters, solvents, masking agents, or acombination of any of the foregoing. As can be appreciated, fillers andadditives employed in a composition may be selected so as to becompatible with each other as well as the polymeric component, curingagent, and or catalyst. Examples of electrically non-conductive fillersinclude materials such as, but not limited to, calcium carbonate, mica,polyamide, fumed silica, molecular sieve powder, microspheres, titaniumdioxide, chalks, alkaline blacks, cellulose, zinc sulfide, heavy spar,alkaline earth oxides, alkaline earth hydroxides, and the like.

Compositions provided by the present disclosure can comprise anelectrically conductive filler. Electrical conductivity and EMI/RFIshielding effectiveness can be imparted to composition by incorporatingconductive materials within the polymer. The conductive elements caninclude, for example, metal or metal-plated particles, fabrics, meshes,fibers, and combinations thereof. The metal can be in the form of, forexample, filaments, particles, flakes, or spheres. Examples of metalsinclude copper, nickel, silver, aluminum, tin, and steel. Otherconductive materials that can be used to impart electrical conductivityand EMI/RFI shielding effectiveness to polymer compositions includeconductive particles or fibers comprising carbon or graphite. Conductivepolymers such as polythiophenes, polypyrroles, polyaniline,poly(p-phenylene) vinylene, polyphenylene sulfide, polyphenylene, andpolyacetylene can also be used. Electrically conductive fillers alsoinclude high band gap materials such as zinc sulfide and inorganicbarium compounds.

Other examples of electrically conductive fillers include electricallyconductive noble metal-based fillers such as pure silver; noblemetal-plated noble metals such as silver-plated gold; noble metal-platednon-noble metals such as silver plated cooper, nickel or aluminum, forexample, silver-plated aluminum core particles or platinum-plated copperparticles; noble-metal plated glass, plastic or ceramics such assilver-plated glass microspheres, noble-metal plated aluminum ornoble-metal plated plastic microspheres; noble-metal plated mica; andother such noble-metal conductive fillers. Non-noble metal-basedmaterials can also be used and include, for example, non-noblemetal-plated non-noble metals such as copper-coated iron particles ornickel plated copper; non-noble metals, e.g., copper, aluminum, nickel,cobalt; non-noble-metal-plated-non-metals, e.g., nickel-plated graphiteand non-metal materials such as carbon black and graphite. Combinationsof electrically conductive fillers can also be used to meet the desiredconductivity, EMI/RFI shielding effectiveness, hardness, and otherproperties suitable for a particular application.

An electrically conductive filler can comprise a metal coated fabricsuch as metal-coated polyester, nylon, spandex, polyolefin, and/oraramids. The metal coating can include a metal such as silver or acombination of metals such as silver/copper, silver/copper/nickel, orsilver/copper/tin.

The shape and size of the electrically conductive fillers used in thecompositions of the present disclosure can be any appropriate shape andsize to impart electrical conductivity and EMI/RFI shieldingeffectiveness to the cured composition. For example, fillers can be ofany shape generally used in the manufacture of electrically conductivefillers, including spherical, flake, platelet, particle, powder,irregular, fiber, and the like. In certain sealant compositions of thedisclosure, a base composition can comprise Ni-coated graphite as aparticle, powder or flake. The amount of Ni-coated graphite in a basecomposition can range from 40 wt % to 80 wt %, or can range from 50 wt %to 70 wt %, based on the total weight of the base composition. Anelectrically conductive filler can comprise Ni fiber. Ni fiber can havea diameter ranging from 10 μm to 50 μm and have a length ranging from250 μm to 750 μm. A base composition can comprise, for example, anamount of Ni fiber ranging from 2 wt % to 10 wt %, or from 4 wt % to 8wt %, based on the total weight of the base composition.

Carbon fibers, particularly graphitized carbon fibers, can also be usedto impart electrical conductivity to compositions of the presentdisclosure. Carbon fibers formed by vapor phase pyrolysis methods andgraphitized by heat treatment and which are hollow or solid with a fiberdiameter ranging from 0.1 micron to several microns, have highelectrical conductivity. As disclosed in U.S. Pat. No. 6,184,280, carbonmicrofibers, nanotubes or carbon fibrils having an outer diameter ofless than 0.1 μm to tens of nanometers can be used as electricallyconductive fillers. An example of graphitized carbon fiber suitable forconductive compositions of the present disclosure include Panex® 3OMF(Zoltek Companies, Inc., St. Louis, Mo.), a 0.921 μm diameter roundfiber having an electrical resistivity of 0.00055 Ω-cm.

The average particle size of an electrically conductive filler can bewithin a range useful for imparting electrical conductivity to apolymer-based composition. For example, the particle size of the one ormore fillers can range from 0.25 μm to 250 μm, or can range from 0.25 μmto 75 μm, or can range from 0.25 μm to 60 μm. A composition of thepresent disclosure can comprise Ketjenblack® EC-600 JD (Akzo Nobel,Inc., Chicago, Ill.), an electrically conductive carbon blackcharacterized by an iodine absorption of 1,000 mg/g to 11,500 mg/g(J0/84-5 test method), and a pore volume of 480 cm³/100 g to 510 cm³/100g (DBP absorption, KTM 81-3504). An electrically conductive carbon blackfiller is Black Pearls® 2000 (Cabot Corporation, Boston, Mass.).

Electrically conductive polymers can be used to impart electricalconductivity or modify the electrical conductivity of compositions ofthe present disclosure. Polymers having sulfur atoms incorporated intoaromatic groups or adjacent to double bonds, such as in polyphenylenesulfide, and polythiophene, are known to be electrically conductive.Other electrically conductive polymers include, for example,polypyrroles, polyaniline, poly(p-phenylene) vinylene, andpolyacetylene. A sulfur-containing prepolymer forming a base compositioncan be polysulfides and/or polythioethers. As such, thesulfur-containing prepolymers can comprise aromatic sulfur groups andsulfur atoms adjacent to conjugated double bonds to enhance theelectrical conductivity of the compositions of the present disclosure.

Compositions of the present disclosure can comprise more than oneelectrically conductive filler and the more than one electricallyconductive filler can be of the same or different materials and/orshapes. For example, a sealant composition can comprise electricallyconductive Ni fibers, and electrically conductive Ni-coated graphite inthe form of powder, particles or flakes. The amount and type ofelectrically conductive filler can be selected to produce a sealantcomposition which, when cured, exhibits a sheet resistance (four-pointresistance) of less than 0.50 Ω/cm², or a sheet resistance less than0.15 Ω/cm². The amount and type of filler can also be selected toprovide effective EMI/RFI shielding over a frequency range of from 1 MHzto 18 GHz for an aperture sealed using a sealant composition of thepresent disclosure.

An electrically conductive base composition can comprise an amount ofelectrically non-conductive filler ranging from 2 wt % to 10 wt % basedon the total weight of the base composition, or can range from 3 wt % to7 wt %. A curing agent composition can comprise an amount ofelectrically non-conductive filler ranging from less than 6 wt % orranging from 0.5% to 4% by weight, based on the total weight of thecuring agent composition.

Galvanic corrosion of dissimilar metal surfaces and the conductivecompositions of the present disclosure can be minimized or prevented byadding corrosion inhibitors to the composition, and/or by selectingappropriate conductive fillers. Corrosion inhibitors include strontiumchromate, calcium chromate, magnesium chromate, and combinationsthereof. U.S. Pat. No. 5,284,888 and U.S. Pat. No. 5,270,364 disclosethe use of aromatic triazoles to inhibit corrosion of aluminum and steelsurfaces. A sacrificial oxygen scavenger such as Zn can be used as acorrosion inhibitor. A corrosion inhibitor can comprise less than 10% byweight of the total weight of the electrically conductive composition. Acorrosion inhibitor can comprise an amount ranging from 2 wt % to 8 wt %of the total weight of the electrically conductive composition.Corrosion between dissimilar metal surfaces can also be minimized orprevented by the selection of the type, amount, and properties of theconductive fillers comprising the composition.

A composition may also include any number of additives as desired.Examples of suitable additives include plasticizers, pigments,surfactants, adhesion promoters, thixotropic agents, fire retardants,masking agents, and accelerators, and combinations of any of theforegoing. When used, the additives may be present in a composition inan amount ranging, for example, from about 0.5% to 60% by weight, wherewt % is based on the total solids weight of the composition. Additivesmay be present in a composition in an amount ranging from about 25 wt %to 60 wt %.

Uses

Compositions provided by the present disclosure may be used, forexample, in sealants, coatings, encapsulants, and potting compositions.A sealant includes a composition capable of producing a film that hasthe ability to resist operational conditions, such as moisture andtemperature, and at least partially block the transmission of materials,such as water, fuel, and other liquid and gases. A coating compositionincludes a covering that is applied to the surface of a substrate to,for example, improve the properties of the substrate such as theappearance, adhesion, wettability, corrosion resistance, wearresistance, fuel resistance, and/or abrasion resistance. A pottingcomposition includes a material useful in an electronic assembly toprovide resistance to shock and vibration and to exclude moisture andcorrosive agents. Sealant compositions provided by the presentdisclosure are useful, e.g., as aerospace sealants and as linings forfuel tanks.

Compositions, such as sealants, may be provided as multi-packcompositions, such as two-pack compositions, wherein one packagecomprises one or more reactive antioxidants and/orantioxidant-containing prepolymers provided by the present disclosureand a second package comprises one or more polyfunctionalsulfur-containing epoxies provided by the present disclosure. Additivesand/or other materials may be added to either package as desired ornecessary. The two packages may be combined and mixed prior to use. Thepot life of the one or more mixed reactive antioxidants and/orantioxidant-containing prepolymers and epoxides is at least 30 minutes,at least 1 hour, at least 2 hours, or more than 2 hours, where pot liferefers to the period of time the mixed composition remains suitable foruse as a sealant after mixing.

Compositions, including sealants, provided by the present disclosure maybe applied to any of a variety of substrates. Examples of substrates towhich a composition may be applied include metals such as titanium,stainless steel, aluminum, and alloys thereof, any of which may beanodized, primed, organic-coated or chromate-coated; epoxy; urethane;graphite; fiberglass composite; Kevlar®; acrylics; and polycarbonates.Compositions provided by the present disclosure may be applied to acoating on a substrate, such as a polyurethane coating. Compositionscomprising antioxidant-containing polythioethers orantioxidant-containing prepolymers provided by the present disclosureexhibit enhanced adhesion to aluminum, aluminum oxide, anodizedaluminum, titanium, titanium oxide, and/or Alodine® surfaces, comparedto similar compositions without an antioxidant.

Compositions provided by the present disclosure may be applied directlyonto the surface of a substrate or over an underlayer by any suitablecoating process known to those of ordinary skill in the art.

Furthermore, methods are provided for sealing a part using a compositionprovided by the present disclosure. These methods comprise, for example,applying a composition provided by the present disclosure to a surfaceof a part, and curing the composition. For example, methods of sealing apart, comprise preparing a curable composition comprising the a reactiveantioxidant or antioxidant-containing prepolymer provided by the presentdisclosure, applying the curable composition to a part; and

curing the curable composition to seal the part.

Parts sealed with a sealant composition of the present disclosure areprovided.

Properties

For aerospace sealant applications it is desirable that a sealant meetthe requirements of Mil-S-22473E (Sealant Class C) at a cured thicknessof 20 mils, exhibit an elongation greater than 200%, a tensile strengthgreater than 250 psi, and excellent fuel resistance, and maintain theseproperties over a wide temperature range from −67° F. to 360° F. Ingeneral, the visual appearance of the sealant is not an importantattribute. Prior to full cure, a sealant provided by the presentdisclosure can have a working time of at least 12 hours, at least 16hours, or at least 20 hours at room temperature. After the sealant ispartially cured and is no longer workable sealants provided by thepresent disclosure can have a tack-free cure time of less than 4 hours,less than 8 hours, less than 12 hours, or less than 24 hours. Workingtime refers to the time period the sealant remains workable orspreadable for application at ambient temperatures after the compositionhas been heated to activate the blocked DBU catalyst. For example, anumerical scale can be used to assess the working time where (1)represents the workability of the initially activated sealant; (2)represents a sealant having a viscosity slightly greater than theinitially activated sealant; (3) represents a sealant having asignificantly greater viscosity than that of the initially activatedsealant; (4) represents a sealant that has begun to gel but remainsspreadable; (5) represents a sealant that has gelled but is no longerspreadable; (6) represents a sealant that has almost cured, but is nottack-free; (7) represents a sealant that is cured to a tack-freecondition; (8) represents a cured sealant having Shore A hardness of20A; (9) represents a cured sealant having Shore A hardness of 35A; and(10) represents a cured sealant having Shore A hardness of 45A.

A composition may be cured under ambient conditions, where ambientconditions refers to a temperature from 20° C. to 25° C., andatmospheric humidity. A composition may be cured under conditionsencompassing a temperature from a 0° C. to 100° C. and humidity from 0%relative humidity to 100% relative humidity. A composition may be curedat a higher temperature such as at least 30° C., at least 40° C., or atleast 50° C. A composition may be cured at room temperature, e.g., 25°C. A composition may be cured upon exposure to actinic radiation, suchas ultraviolet radiation. As will also be appreciated, the methods maybe used to seal apertures on aerospace vehicles including aircraft andaerospace vehicles.

A composition can achieve a tack-free cure in less than about 2 hours,less than about 4 hours, less than about 6 hours, less than about 8hours, or in less than about 10 hours, at a temperature of less thanabout 200° F.

The time to form a viable seal using curable compositions of the presentdisclosure can depend on several factors as can be appreciated by thoseskilled in the art, and as defined by the requirements of applicablestandards and specifications. In general, curable compositions of thepresent disclosure develop adhesion strength within 24 hours to 30hours, and 90% of full adhesion strength develops from 2 days to 3 days,following mixing and application to a surface. In general, full adhesionstrength as well as other properties of cured compositions of thepresent disclosure becomes fully developed within 7 days followingmixing and application of a curable composition to a surface.

Cured compositions disclosed herein, such as cured sealants, exhibitproperties acceptable for use in aerospace applications. In general, itis desirable that sealants used in aviation and aerospace applicationsexhibit the following properties: peel strength greater than 20 poundsper linear inch (pli) on Aerospace Material Specification (AMS) 3265Bsubstrates determined under dry conditions, following immersion in JetReference Fluid (JRF) Type I for 7 days, and following immersion in asolution of 3% NaCl according to AMS 3265B test specifications; tensilestrength between 300 pounds per square inch (psi) and 400 psi; tearstrength greater than 50 pounds per linear inch (pli); elongationbetween 250% and 300%; and hardness greater than 40 Durometer A. Theseand other cured sealant properties appropriate for aviation andaerospace applications are disclosed in AMS 3265B, which is incorporatedby reference in its entirety. It is also desirable that, when cured,compositions of the present disclosure used in aviation and aircraftapplications exhibit a percent volume swell not greater than 25%following immersion for one week at 60° C. (140 ° F.) and ambientpressure in JRF Type I. Other properties, ranges, and/or thresholds maybe appropriate for other sealant applications.

Compositions provided by the present disclosure are fuel-resistant. Asused herein, the term “fuel resistant” means that a composition, whenapplied to a substrate and cured, can provide a cured product, such as asealant, that exhibits a percent volume swell of not greater than 40%,in some cases not greater than 25%, in some cases not greater than 20%,in yet other cases not more than 10%, after immersion for one week at140° F. (60° C.) and ambient pressure in Jet Reference Fluid (JRF) TypeI according to methods similar to those described in ASTM D792 (AmericanSociety for Testing and Materials) or AMS 3269 (Aerospace MaterialSpecification). Jet Reference Fluid JRF Type I, as employed fordetermination of fuel resistance, has the following composition:toluene: 28%±1% by volume; cyclohexane (technical): 34%±1% by volume;isooctane: 38%±1% by volume; and tertiary dibutyl disulfide: 1%±0.005%by volume (see AMS 2629, issued Jul. 1, 1989, § 3.1.1, etc., availablefrom SAE (Society of Automotive Engineers)).

Compositions provided herein provide a cured product, such as a sealant,exhibiting a elongation of at least 100% and a tensile strength of atleast 400 psi when measured in accordance with the procedure describedin AMS 3279, § 3.3.17.1, test procedure AS5127/1, § 7.7.

Compositions provide a cured product, such as a sealant, that exhibits alap shear strength of greater than 200 psi, such as at least 220 psi, atleast 250 psi, and, in some cases, at least 400 psi, when measuredaccording to the procedure described in SAE AS5127/1 paragraph 7.8.

A cured sealant comprising a composition provided by the presentdisclosure meets or exceeds the requirements for aerospace sealants asset forth in AMS 3277.

Apertures, including apertures of aerospace vehicles, sealed withcompositions provided by the present disclosure are also disclosed.

A cured sealant provided by the present disclosure exhibits thefollowing properties when cured for 2 days at room temperature, 1 day at140° F. and 1 day at 200° F.: a dry hardness of 49, a tensile strengthof 428 psi, and an elongation of 266%; and after 7 days in JRF Type I, ahardness of 36, a tensile strength of 312 psi, and an elongation of247%.

Compositions provided by the present disclosure exhibit a Shore Ahardness (7-day cure) greater than 10, greater than 20, greater than 30,or greater than 40; a tensile strength greater than 10 psi, greater than100 psi, greater than 200 psi, or greater than 500 psi; an elongationgreater than 100%, greater than 200%, greater than 500%, or greater than1,000%; and a swell following exposure to JRF Type I (7 days) less than20%.

EXAMPLES

The present invention is further illustrated by reference to thefollowing examples, which describe the synthesis, properties, and usesof certain polythiol adducts, prepolymers formed using the polythioladducts, compositions comprising the prepolymers and cured sealantsprepared using compositions. It will be apparent to those skilled in theart that many modifications, both to materials, and methods, may bepracticed without departing from the scope of the disclosure.

Example 1 Synthesis of Polythiol Adducts

1,5-Dimercapto-3-thiapentane (DMDS) and methyl ethyl ketone (MEK) werereacted in a 2:1 molar ratio in the presence of para-toluene sulfonicacid (p-TsOH) and cyclohexane as a co-solvent at a temperature from 90°C. to 95° C. to provide a polythiol adduct. The reaction was continueduntil the ketone infrared peak at 1713 cm⁻¹ was no longer present. Thepolythiol adduct was present as a water-clear liquid.

Alternatively DMDS and MEK were reacted in a 3:2 molar ratio to providean extended polythiol adduct.

A thiol-terminated urethane-extended adduct was obtained by reacting thepolythiol adduct with Desmodur® W (H₁₂MDI diisocyanate) in a 2:1 ratioin the presence of dibutyl tin dilaurate (DBTL) catalyst at atemperature from 75° C. to 95° C. for 27 h. The product was solid atroom temperature.

Example 2 Synthesis of Isocyanate-Terminated Urethane-ContainingPrepolymers

A thiol-terminated polysulfide prepolymer (Thioplast® G-112 or Thiokol®L-32), the polythiol adduct of Example 1, and a diisocyanate (H₁₂MDI)were combined and heated to a temperature of 70° C. in the presence of aPolycat® 8 catalyst to provide an isocyanate-terminatedurethane-containing prepolymer. The equivalent ratio of thethiol-terminated polysulfide prepolymer to polythiol adduct was from 2:5to 1.5:4, such as 1:3. The ratio of diisocyanate equivalents to thiolequivalents was from 5:1 to 2:1.

Example 3 Synthesis of Isocyanate-Terminated Urethane-ContainingPrepolymers

In two-step method of preparing an isocyanate-terminatedurethane-containing prepolymer, a diisocyanate (H₁₂MDI) and athiol-terminated polysulfide prepolymer (Thioplast® G-112 or Thiokol®L-32) were combined and heated to a temperature of 70° C. to 75° C. inthe presence of Polycat® 8 catalyst (N,N′-dimethylcyclohexylamine) toprovide an isocyanate-terminated polysulfide prepolymer.

In a second step, the polythiol adduct of Example 1 was combined withthe isocyanate-terminated polysulfide prepolymer in the first step and adiisocyanate, and the mixture reacted at a temperature of 70° C. to 75°C. in the presence of Polycat® 8 catalyst to provide anisocyanate-terminated urethane-containing prepolymer.

The ratio of isocyanate equivalents to thiol equivalents was from 5:1 to2:1.

Example 4 Low Density Sealant Compositions

To prepare a low density sealant composition, Expancel® microsphereswere combined with a liquid polyamine, (Jefflink® 754), in the presenceof less than 10 wt % of ethyl acetate and/or butyl acetate to provide ahomogeneous mixture of polyamine-coated low density microspheres. Themixture was dried in an oven to produce a dry powder.

The polyamine-coated low density microspheres were then combined withthe isocyanate-terminated urethane-containing prepolymer of Example 2 orExample 3 and a low boiling point solvent.

The curable composition was poured into a Teflon® mold and cured for 16hours at room temperature. The cured sealant exhibited a Shore Ahardness of 50 and a Shore D hardness of 12. The cured film had adensity of 0.73 g/L. The cured sealant passed the NaCl immersionresistance and aviation fluid resistance tests according to AS 5127/1C.

Finally, it should be noted that there are alternative ways ofimplementing the embodiments disclosed herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive.Furthermore, the claims are not to be limited to the details givenherein, and are entitled their full scope and equivalents thereof.

What is claimed is:
 1. A polythiol adduct comprising the condensationreaction products of reactants comprising: a polythiol; and a ketone. 2.The polythiol adduct of claim 1, wherein the polythiol adduct has athiol functionality from 2 to
 6. 3. The polythiol adduct of claim 1,wherein the polythiol comprises a dithiol, wherein the dithiol comprisesdimercaptodiethylsulfide (DMDS), 3,6-dioxa-1,8-octanedithiol (DMDO), ora combination thereof.
 4. The polythiol adduct of claim 1, wherein theketone comprises propan-2-one, methyl ethyl ketone (butan-2-one),pentan-2-one, hexan-2-one, pentan-3-one, 3-methylbutan-2-one,3-methylpentan-2-one, 4-methylhexan-3-one, 2-methylpentan-3-one,2,4-dimethylpentan-3-one, or a combination thereof.
 5. The polythioladduct of claim 1, wherein: the polythiol comprisesdimercaptodiethylsulfide, 3,6-dioxa-1,8-octanedithiol, or a combinationthereof; and the ketone comprises methyl ethyl ketone.
 6. The polythioladduct of claim 1, wherein, the polythiol comprises a dithiol having thestructure of Formula (1):HS—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—SH  (1) wherein, each R³ is selectedfrom hydrogen oand methyl; each X is independently selected from O andS; p is an integer from 2 to 6; q is an integer from 1 to 5; and r is aninteger from 2 to 10; and. the ketone comprises a ketone having thestructure of Formula (3):R⁴—C(═O)—R⁴  (3) wherein each R⁴ is independently selected from C₁₋₅alkyl.
 7. The polythiol adduct of claim 6, wherein each R³ is hydrogen.8. The polythiol adduct of claim 6, wherein at least one R³ is methyl.9. The polythiol adduct of claim 6, wherein: p is selected from 2 and 3;q is selected from 1 and 2; and r is selected from 2 and
 3. 10. Thepolythiol adduct of claim 6, wherein: each R³ is hydrogen; and each ofp, q, and r is
 2. 11. The polythiol adduct of claim 6, wherein each R⁴is independently selected from methyl, ethyl, n-propyl, n-butyl,n-pentyl, isopropyl, sec-butyl, pentan-2-yl, 2-methylbutyl, isopentyl,3-metylbutan-2-yl, and isobutyl.
 12. The polythiol adduct of claim 6,wherein each R⁴ is independently selected from methyl and ethyl.
 13. Thepolythiol adduct of claim 6, wherein one R⁴ is methyl and the other R⁴is selected from methyl and ethyl.
 14. The polythiol adduct of claim 6,wherein the dithiol of Formula (2) comprises a dithiol of Formula (2a),a dithiol of Formula (2b), or a combination thereof:HS—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—SH  (2a)HS—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—SH  (2b)
 15. The polythiol adduct ofclaim 14, wherein each of p, q, and r is
 2. 16. A polythiol adducthaving the structure of Formula (6):HS—(—R¹—S—R²—S—)_(n)—R¹—SH  (6) wherein, n is an integer from 1 to 10;each R¹ is independently selected from a moiety of Formula (1a):—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a) wherein, each R³ is selectedfrom hydrogen and methyl; each X is independently selected from O and S;p is an integer from 2 to 6; q is an integer from 1 to 5; and r is aninteger from 2 to 10; and each R² independently is a moiety having thestructure of Formula (3a):—C(—R⁴)₂—  (3a) wherein each R⁴ independently comprises C₁₋₅ alkyl. 17.The polythiol adduct of claim 16, wherein the polythiol adduct comprisesa dithiol having the structure of Formula (4):H—{—S—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—SH  (4)18. The polythiol adduct of claim 16, wherein the polythiol adductcomprises a dithiol having the structure of Formula (4a), a dithiolhaving the structure of Formula (4b), or a combination thereof:H—{—S—[—(CHR³)_(p)—S—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—S—]_(q)—(CHR³)_(r)—SH  (4a)H—{—S—[—(CHR³)_(p)—O—]_(q)—(CHR³)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CHR³)_(p)—O—]_(q)—(CHR³)_(r)—SH  (4b)19. The polythiol adduct of claim 18, wherein: each of p, q, and r is 2;each R⁴ is independently selected from methyl and ethyl, and each R³ isselected from hydrogen and methyl.
 20. The polythiol adduct of claim 6,wherein the polythiol adduct comprises a dithiol having the structure ofFormula (5), a dithiol having the structure of Formula (5a), a dithiolhaving the structure of Formula (5b); or a combination of any of theforegoing:H—{—S—[—(CH₂)_(p)—X—]_(q)—(CH₂)_(r)—X—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—X—]_(q)—(CH₂)_(r)—SH  (5)H—{—S—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—S—]_(q)—(CH₂)_(r)—SH  (5a)H—{—S—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—S—C(R⁴)₂—}_(n)—S—[—(CH₂)_(p)—O—]_(q)—(CH₂)_(r)—SH  (5b)
 21. The polythiol adduct of claim 20, wherein: each of p, q, and ris 2; and each R⁴ is independently selected from methyl and ethyl.
 22. Acomposition comprising the polythiol adduct of claim
 1. 23. Acomposition comprising the polythiol adduct of claim
 16. 24. Aprepolymer, wherein the prepolymer comprises at least one segment havingthe structure of Formula (6a),—(—R¹—S—R²—S—)_(n)R¹—  (6a) wherein, n is an integer from 1 to 10; eachR¹ is independently a moiety having the structure of Formula (1a):—[—(CHR³)_(p)—X—]_(q)—(CHR³)_(r)—  (1a) wherein, each R³ isindependently selected from hydrogen and methyl; each X is independentlyselected from O and S; p is an integer from 2 to 6; q is an integer from1 to 5; and r is an integer from 2 to 10; each R² independentlycomprises a moiety having the structure of Formula (3a):—C(—R⁴)₂—  (3a) wherein each R⁴ is independently selected from C₁₋₅alkyl.
 25. A composition comprising the polythiol adduct of claim 24.